Abstract: The destruction of the Islamic State has left the U.S.-backed Syrian Democratic Forces holding thousands of foreign fighters who joined the Islamic State’s ranks from abroad as well as members of their families. What happens to these detainees will impact the continuing jihadi campaign in the Middle East and beyond, but legal constraints, fears of terrorism, already overburdened security forces, widespread public hostility toward Muslims in general, intensified by the barbaric behavior of the Islamic State, complicate discussions of what to do next. This essay, which reflects the author’s personal views, examines eight options and is intended to move the discussion beyond political bickering and wishful thinking. Preferred solutions may not be achievable. Endless delay could prove dangerous.

As the last bastions of the Islamic State fell in Syria, thousands of the group’s fighters surrendered to the advancing Syrian Democratic Forces (SDF), a U.S.-backed paramilitary force comprised mainly of Kurdish militias along with a number of smaller Arab formations. The numbers have grown rapidly, swelled by refugees who fled as the last towns held by the Islamic State fell and as more fighters surrendered or were captured.

The counts and categories remain slippery. According to United Nations officials, the main SDF camp at Al Hol, as of April 18, 2019, held an estimated 75,000 persons, 65,000 of whom had arrived in the previous 100 days.1 Of these, 43 percent are Syrians, 42 percent are Iraqis, and 15 percent are foreigners. Ninety percent are women and children; children alone account for 66 percent of the total.2

According to one report in March 2019, the SDF held 8,000 Islamic State fighters, including 1,000 foreign fighters in its prisons.3 (Syrians who were recruited or impressed into the ranks of the Islamic State were allowed to change sides and fight in the ranks of the SDF or were sent home.4) The number of foreign fighters continues to change. On February 18, 2019, the SDF claimed that it held 800 foreign fighters.5 Another source put the number at 1,000.6 But other reports in March and April suggested that the number of suspected foreign fighters could be 2,000 or more.7 In addition to the foreign fighters, there are thousands of their wives and children.8

The changing totals reflect a fluid situation as the refugees and detainees are sorted out. Children are being born in the Al Hol camp—and some die. Some of the foreign fighters try to conceal their identity. But the lack of clarity on the numbers also reflects the chaos of the region following the territorial demise of the Islamic State. The situation is still unstable, which poses risks.9

What the world does or does not do about these foreign fighters and their families could affect the future stability of the region and the countries from which the foreign volunteers came. Will policies be guided by the parables of recovery and return or by calculations of risk?

Are the foreign fighters and their families lost sheep to be recovered and returned to the fold? Are they turncoats who deserve to be cast out and forever banished beyond the nation’s walls? Were they dragged along by fanatic fathers and husbands or lured into the jihadi maelstrom by adolescent illusions of romance and adventure? Are they torturers and murderers who must be punished for their crimes? Are they unrepentant fanatics bent upon avenging their defeat? Are they villains or victims? Future terrorists or reclaimable allies in dissuading others from following their path? Subjects for rehabilitation or beyond redemption?

The human debris of the Islamic State probably includes all of these scenarios. Sorting out their motives for traveling to Syria, their roles in the ranks of the Islamic State and experience living under Islamic State rule, and their current attitudes and apparent readiness to atone will assist in making judgments. But can their intentions ever be known with certainty?

U.S. Secretary of State Mike Pompeo stated on May 8, 2019, that “we have an expectation that every country will work to take back their foreign fighters and continue to hold those foreign fighters, we think that is essential,”10 but Britain’s home secretary Sajid Javid vowed that he “will not hesitate” to prevent the return of Britons who traveled to join the Islamic State.11

A former head of the British army, General Lord Dannett, has argued that Britain’s foreign fighters in Syria must be brought back to the United Kingdom because they are the United Kingdom’s responsibility. “They have got to be held while they are talked to and if there is sufficient evidence against any of them … they have to be put through due process and imprisoned if that is the right thing to do. But I think it is also important that we treat them fairly with justice and tempered with a bit of mercy as well because … the way we treat them may well have important significance for the way other people view our society.”12 Other security officials who agree that foreign fighters from their countries should be repatriated and investigated add that, personally, they do not want to see them come back.13

Public attitudes, partisan politics, domestic and international law, the probability of successful prosecution, the potential risk to public safety, and humanitarian concerns (though, for most, a secondary concern) all influence and complicate policy decisions. Some countries have already addressed this issue in an ad hoc manner, but there is still no overall strategy or plan.

The challenge is to create a comprehensive approach to deal with a large number of individuals according to individual circumstances and with a lot of unknowns. By resolving each case in a transparent process in accordance with the law, bringing terrorists to justice while assisting those who are the victims of Islamic State terror, the United States and its allies can portray the defeat of the Islamic State not as a military victory, but the outcome of successful counterterrorism policies.

This essay examines the pros and cons of various options that have been put forward for dealing with the foreign fighters and their families. It is intended to provoke comment and, hopefully, move the discussion toward pragmatic measures by providing a hard surface for concrete debate. The essay concludes that there is no obvious single solution, but there are some immediate actions that can improve the situation. As a first step, however, it is important to appreciate the complexity of the problem.14

A Diverse Population
The inhabitants crowded into the SDF camps comprise a diverse population. Displaced townspeople and villagers who were able to flee from Islamic State-held towns as battlelines grew nearer appear to be the closest to genuine refugees. Many can be described as victims of the Islamic State’s cruel occupation, but as in previous wars, others among them may have been collaborators. Some of the latter, no doubt, acted under duress—the Islamic State viciously punished any resistance to its rule—but others may have shared the jihadis’ ideology or profited from its presence. Still others may fit somewhere in the middle, thus further complicating the situation.

Those judged to be genuine refugees can be dealt with through existing channels, but that still requires some vetting to sort out those who were combatants or willing supporters from those who were innocent bystanders, which is not so easily done. The numbers are slippery and the divisions murky.

Those who actively supported the Islamic State when it ruled the land will provide the support structure for a continuing underground fight, but trying to segregate Islamic State victims from Islamic State collaborators may not be possible and certainly will not be easy. One question of immediate concern is whether unidentified Islamic State supporters may be intimidating other residents in the camps. Is repudiating the Islamic State dangerous?

The attitudes of the fighters themselves also vary. Some presumably remain convinced jihadis, determined to continue the armed struggle if they can. Others, disillusioned by their experience, may desire only to return home and lead normal lives.

The families of the fighters themselves also represent a diverse group. In a number of respects, the wives and widows of Islamic State fighters represent a thornier problem than the fighters. Some of them were brought to Syria by their husbands; others traveled to Syria seeking jihadi husbands. Their experiences and their attitudes vary greatly. Some suffered terrible ordeals. They married into continuing captivity although with different warders. They were exchanged as sex slaves or assigned to new partners as previous spouses were killed off.

In accord with salafi ideology, most women were confined to purely domestic roles. Others, however, became active participants in special units that enforced Islamic State rule and were involved in the abuse of other women, including the enslaved Yazidis.15

Their ideological commitment varies from traumatized victims to committed fanatics who will indoctrinate their children and others they come into contact with—a continuing source of radicalization and violence. In 2016, an all-female cell attempted to carry out a terrorist attack in France.16 Another all-female cell was arrested for plotting a terrorist attack in the United Kingdom.17 (None of them had traveled to Syria, although at least one had indicated a desire to go.) These incidents have hardened attitudes toward women.

The children pose an even greater challenge, perhaps the greatest challenge of all. Infants and toddlers have no appreciation of ideologies. They must be regarded as innocents, although the older ones may require counseling to address what they have witnessed and suffered and were taught in Islamic State schools and training camps. Traditionally, international law has regarded children as victims rather than perpetrators, but this view has begun to change precisely because of how the Islamic State and other irregular military formations have deliberately enlisted children in their violent campaigns.18 Islamic State videos, for example, depicted children ostensibly executing prisoners or holding up the heads of decapitated victims. These were not just exceptional events staged for propaganda purposes, but were part of a systematic effort to inculcate brutality among succeeding generations. The Islamic State was widely reported to have forcibly sent children as young as 13 to training camps where, after showing pupils videos of actual beheadings, instructors distributed large knives and “infidel” dolls with blond hair and blue eyes dressed in orange jumpsuits (like the Western hostages beheaded by the Islamic State). The young students then were shown how to properly hold their knives to decapitate the dolls.19 This experience will doubtlessly affect their mental and emotional well-being, especially their ability to adjust to very different norms.

A discarded Islamic State flag is pictured on the ground in the village of Baghouz in Syria’s eastern Deir ez-Zor province near the Iraqi border on March 24, 2019, a day after the group’s ‘caliphate’ was declared defeated by the U.S.-backed Kurdish-led Syrian Democratic Forces (SDF). (Giuseppe Cacace/AFP/Getty Images)

Action is Necessary
Despite the difficulties in doing so, it is imperative to separate and assist genuine victims while identifying those who remain committed jihadis—men and women—and preventing them from escaping to new jihadi fronts or bringing them home and turning them loose to commit terrorist attacks or recruit new generations of fighters. The April 2019 church and hotel bombings in Sri Lanka underscore the continuing resonance and spread of jihadi ideology. The territory held by the Islamic State has been recaptured, but the contest is not over and will not end until the jihadi chain has been broken.

In late April 2019, the Islamic State carried out a series of attacks that in two days killed more than 60 Syrian soldiers and militiamen, demonstrating the resilience of the group.20 The ability to carry out large attacks raises the risk of mass jailbreaks. In 2013, the Islamic State’s predecessor group freed 500 inmates, including a number of its senior commanders, in simultaneous attacks on two prisons in Iraq,21 and in 2015, al-Qa`ida in the Arabian Peninsula attacked a jail in Yemen, freeing 300 prisoners.22 Those now held by the SDF must be secured.

There is also the longer-term threat. Each new jihadi front has its origins in the previous conflict and, in turn, promotes the next jihad. Foreign fighters who joined the Afghan resistance against the Soviet invasion in the 1980s went on to participate in the wars in Bosnia, Chechnya, and Afghanistan in the 1990s. Veterans of al-Qa`ida’s operations in Afghanistan in the 1990s scattered to launch jihadi terrorist campaigns from Indonesia to Morocco in the early 2000s while others joined the Iraqi insurgency following the 2003 U.S.-led occupation to form the core of what later became the Islamic State.

The Islamic State is different in having attracted tens of thousands of foreign fighters, including thousands of volunteers from Western countries. A study by The International Centre for the Study of Radicalisation (ICSR) at King’s College in London reported that by June 2018, 41,490 persons from 80 countries had joined the Islamic State in both Iraq and Syria.23 (Thirteen percent of these were women and 12 percent were minors.) These are remarkably precise numbers, but should not imply knowledge is exact.

Middle Eastern and North African countries provided 45 percent of the volunteers with another 20 percent coming from Central, South, East, and Southeast Asia. More than 17 percent came from Eastern Europe, including many from the Russian Caucasus; another 14 percent came from Western Europe, mainly France, Germany, the United Kingdom, and Belgium, which together accounted for more than 70 percent of those coming from Western European countries. Less than two percent came from the Americas, Australia, and New Zealand.a

According to the ICSR study, 272 travelers came from the United States. Public estimates run as high as 300, but this was an all-in figure that included those who tried to travel to Syria but who were intercepted before departure, were arrested before arriving in Syria, or failed to connect with a group or changed their mind and returned. Approximately 41 percent were intercepted before departing the United States. As many as 40 travelers may still be at large, including those who traveled to various jihadi fronts up to 10 years ago, but many of those unaccounted for are probably dead.24

Of the 41,490 foreign fighters in Syria, the ICSR study reports that 7,366 (or about 18 percent) have returned to their country of origin, including 1,765 (or 30 percent) of the 5,904 who originally departed from Western Europe.25 According to an August 2018 United Nations report, “Member States noted that flows of returnees and relocators from Iraq and the Syrian Arab Republic had not materialized to the degree expected, but the vast majority of those who had successfully left the conflict zone had returned home rather than relocating elsewhere.”26 However, while countries might know or at least have a good idea of how many foreign fighters came home, it is not clear that they would necessarily have complete information about foreign fighters who managed to evade capture and relocate to other jihadi fronts. Also, the U.N. report was issued in August 2018 and based upon earlier reported numbers. Therefore, it would not reflect the final days of intense conflict that marked the end of the Islamic State.

Only rough estimates are possible of how many foreign fighters remain at large. According to the most informed assessment, the attrition rate of foreign fighters in the Islamic State could be around a third, which would leave more than 25,000 still alive.27 Whether they are still active is another matter. Assuming that approximately a third of the European fighters were killed, and approximately 30 percent have already returned, then more than 2,000 Western fighters could be presumed to be alive, a few more adding Americans and Australians, but these are extrapolations from estimates and not a reliable tally. There is considerable uncertainty what casualty rates were in the final defenses of the Islamic State or where the survivors may be.

The Islamic State suffered heavy casualties as it defended its last redoubts against air and ground assault. Although some foreign fighters rose to leadership positions, the Islamic State treated many of its foreign fighters as expendable, and those who played prominent roles and could be identified were a priority target for the U.S.-led coalition fighting the Islamic State—a number were killed in drone strikes. Some may have migrated to other rebel formations in Syria or other Islamic State fronts outside of Syria. Others were captured by Iraqi or Syrian forces or by the SDF. Some former foreign fighters may be in jail or hiding out in Turkey. It must be assumed that some may have successfully evaded the authorities and are lying low at home. Some are simply missing in action and will never be accounted for.

It is tempting to portray many of those who traveled to the Islamic State as yesterday’s fools, deserving their own misfortune. But left on their own, the survivors could become tomorrow’s fanatics.

One earlier study of Westerners who participated as fighters on jihadi fronts between 1990 and 2010 concluded that one in nine foreign fighters returned for an attack in the West.28 A subsequent study showed that one in 11 jihadi terrorists in the West had previously fought in the ranks or received training from jihadi groups abroad.29 This study, however, also showed that of 26 terrorist plots in Europe, five “contained at least one individual who can be categorized as a genuine foreign fighter (that is, having joined a jihadi group to fight in its ranks) whereas eight plots … had a link to a Western individual who went to a terrorist training camp.”30 Thus, as noted by the study, experience abroad figured in half of the plots,31 although most of the plotters were not former foreign fighters but individuals who can best be categorized as foreign trainees—that is, individuals who specifically traveled abroad to obtain training and possible assistance to carry out terrorist plots at home.

According to the author’s own research, of the 281 individuals who traveled abroad or attempted to travel abroad from the United States to join jihadi fronts or obtain training for terrorist plots at home between 9/11 and October 2018, only 28—one in 10—made it to their foreign destination, connected with a jihadi group, and returned to participate in a terrorist plot in the United States, and only one carried out a terrorist attack.32 b This was Faisal Shahzad, who in 2010 attempted to detonate a car bomb in New York’s Time Square. However, 18 percent of those who actually connected with a jihadi group returned to participate in a terrorist plot. All but one of these plots occurred before 2010. Authorities are now more alert to intercepting foreign travelers on their way out or as they attempt to return. As will be detailed later in this article, only one of the post-2011 travelers has been involved in a terrorist plot in the United States after returning. Almost all of the Islamic State returnees to the United States are in jail.33

The bloody terrorist campaign in Belgium and France in 2015 and 2016—including the terrorist attacks in Paris in November 2015, which left 130 persons dead, and in Brussels in March 2016, in which another 32 people died—appeared to underscore the increased threat posed by jihadis returning from Syria. This campaign was carried out by a network revolving around Abdelhamid Abaaoud, a Belgian national of Moroccan descent who traveled to Syria to join the Islamic State in 2013.34 It appears that Abaaoud’s primary purpose was not to fight in Syria, but to recruit arriving Belgian and French foreign fighters for operations back home. He was also able to draw upon the support of radicalized confederates who had remained at home. They provided the hideouts, logistical support, weapons, and reinforcements to Abaaoud’s operatives sent back from Syria. Many of Abaaoud’s confederates came from the criminal underworld and knew how to obtain and operate firearms. To this, they added bomb-making skills obtained in Syria. The returnees, compared to those who had remained at home, more willingly accepted death. They carried out almost all of the suicide bombings and when cornered, often fought to the death.35

Whether the Abaaoud network should be regarded as a unique one-off phenomenon or an indicator of a new dimension of the threat remains a matter of conjecture. Abu Bakr al-Baghdadi has continued to exhort his followers to carry out attacks in the West, however, the Islamic State no longer has an influx of foreign fighters who can be turned around to launch attacks in Europe or the United States. Islamic State-inspired terrorist attacks have continued in Europe and the United States although the pace has declined since the peak years of 2015-2016,36 and many of these have been carried out by lone perpetrators and involve primitive—though still deadly— tactics such as car rammings and stabbings, for which no training is required.c

However, the April 2019 terrorist attacks in Sri Lanka, in which more than 250 persons died, again demonstrated at the very least that the Islamic State-inspired terrorist campaign continues on a global level. At least one of the bombers had reportedly traveled to Syria, and according to one senior Sri Lankan police official, the Sri Lankan bombers acquired their technical skills from the Islamic State.37 If these reports are confirmed, it would underscore the threat posed by the returnees. It is terrorist spectaculars, not statistics that drive public perceptions of the threat—and, in turn, influence the decisions of political leaders.

Bringing back captured jihadi volunteers is not a humanitarian obligation; it serves the long-term goal of defeating the jihadi enterprise and ensuring that it does not easily rise again. The foreigners in Syria should be returned and cleared or prosecuted and incarcerated; if that is not possible in every case, they must at least be monitored. There should be no illusions that the task will be easy or straightforward.

Justice must be done. Those who are guilty of atrocities should be prosecuted for their crimes, which include mass murders and the kidnapping and beheading of hostages, including Americans. At the same time, the captives are a potential resource, able to provide information about the Islamic State—especially its recruiting—and evidence needed for other prosecutions.d If truly repentant, they can also be enlisted in efforts to dissuade young people from repeating their own mistakes. The degree of cooperation would affect their sentences. However, their full cooperation cannot realistically be expected until they are removed from their current circumstances in Syria. They are in camps, mixed in with hardened fanatics who could still threaten those who betray the cause.e So long as they fear being left behind in Syria, concerns about their survival may discourage cooperation.

Finally, this is a messaging opportunity not to be missed. In contrast to the mass executions, beheadings, and crucifixions that the Islamic State advertised as justice, the United States and other countries in the international coalition fighting the Islamic State could display their values.

If doing something is necessary, what then are the options?38

The Options
Turn them loose.
Under International Humanitarian Law, prisoners of war must be released and repatriated without delay after the end of hostilities. (This would not apply to those who may have committed war crimes.) However, for other types of detainees, international law only recommends—but does not impose—their release at the end of the conflict. The law requires the release of persons deprived of liberty as a consequence of hostilities only when the reasons which necessitated their internment no longer exist and then as soon as possible after the end of hostilities.39

But have hostilities ended? Although the broader rebellion in Syria and Iraq has been contained and the territory initially seized by the Islamic State has been recovered, its leaders and many of its fighters remain at large. Forced to operate underground, they have slipped back into villages where they reportedly have formed cells that will continue the armed struggle.40 Meanwhile, the Islamic State continues to exercise a measure of coercive influence in areas it lost; Islamic State websites continue to promote its global armed struggle abroad; individuals continue to mount attacks in the name of the Islamic State; and organized Islamic State fronts continue to fight in a number of countries outside Syria.f

The Islamic State’s foreign fighters have already demonstrated their willingness to leave their countries of residence and travel to a conflict zone to participate in armed jihad, which they regard as a global campaign. These foreign fighters—in particular, those from the West—will tend not to be able to blend into the local population and survive as underground fighters. They can, however, redeploy to another front. This has been a feature of the history of global jihad, with fighters migrating from battlefield to battlefield. The global conflict is not over and may not be over for many years.g

President Trump threatened to turn the Islamic State detainees loose.41 Simply releasing the detainees would be dangerous and is not a realistic option. President Trump’s threat appears to have been an expression of irritation calculated to persuade European countries to repatriate their own nationals.

Kurdish officials have warned that they have no capacity to hold the detainees indefinitely.42 Meanwhile, President Trump announced the departure of U.S. troops from Syria. Although U.S. officials subsequently indicated that a residual force will remain, there is uncertainty about the continued U.S. commitment.43 h Withdrawal may signal a decline in U.S. support for the SDF. While turning the detainees loose is not an option, it could be an unintended consequence of inattention.

Take away their citizenship and leave them in the ‘desert.’
This idea has gained ground in Europe, which is already divided on the acceptance of large numbers of refugees and immigrants from the Middle East and Africa. The idea of bringing back those viewed as dedicated jihadis is unpopular, especially where there is uncertainty about the ability to prosecute or control them. If not put in prison, they will be able to travel freely throughout Europe’s Schengen zone, creating potential security problems even for countries that did not send large numbers of volunteers to Syria. Currently, Europe has trouble monitoring those already under surveillance.

Stripping individuals of their citizenship and leaving them in Syria has political and emotional appeal. It sounds tough, although merely taking away citizenship of those who committed terrible atrocities hardly seems like justice. It also reduces the potential risk to political leaders that a returnee will escape justice—or serve a short sentence—and then carry out a terrorist attack. While most of the returnees can be adjudicated properly, if only one of them goes on to carry out a terrorist attack, it would be politically disastrous to anyone who supported repatriation. The inclination is to kick the can down the road.

Removing citizenship raises the risk that the Islamic State detainees will be released or escape, creating potential new threats. But it may be perceived there is less political risk in such an approach. If, in the future, some left-behind Islamic State veterans sneak back into their country and kill people, it can be presented by politicians as the failure of those charged with intelligence or border security, not those who banished the fighters to remain abroad. And as for their possible continued role in the global jihad, stripped of their citizenship, they are anonymous fighters, no longer nationals of the country and therefore no longer the responsibility of its government. (And if they migrate to other jihadi fronts, it is likely that more of them may be killed.)

It is a cynical calculation that contradicts the basic principle that nation states have committed to in their approach to terrorism: that terrorism constitutes a threat to international peace and security and there is no unilateral solution. Therefore, the international community has agreed to cooperate in its suppression. Stripping of citizenship assumes the terrorist will go away if he or she is no longer our problem, but is instead someone else’s problem. Finally, removing nationality can go against international law.44

On a practical basis, the lack of a U.S. or European passport does not prevent but will make it more difficult for denaturalized individuals to sneak back into the country, especially as border controls have become more sophisticated. But it may also maroon once foolish, now repentant individuals, who are likely to be embittered and re-radicalized. Putting aside the principle of international cooperation against terrorism, from a purely national security perspective, the judgment is whether the danger posed by repatriated fighters is greater than that posed by a floating population of rootless jihadis.

Several recent cases of denaturalization have made headlines, provoking broad public debate. In February 2019, the British government removed the citizenship of Shamima Begum, a girl who traveled to Syria in 2015 when she was 15 and who wanted to return to the United Kingdom with her newborn infant.45 (The newborn died three weeks after birth in the camp.) Her return was prevented by the Home Office, whose spokesman stated that the “priority is the safety and security of Britain and the people who live there.” In order to protect the country, the Home Secretary “has the power to deprive someone of their citizenship where it would not render them stateless.”46 (According to the Home Office, Begum’s parents are from Bangladesh so she could apply to that country for citizenship.) The decision has been challenged in court.

In a similarly controversial pronouncement, the United States in February 2019 declared that Hoda Muthana, another young woman who traveled to Syria in 2015 and now wishes to return home with her children, was never a U.S. citizen.47 Although born in the United States to parents from Yemen, her father was in the country at the time on a diplomatic passport, which excludes her from automatic citizenship. It is a technicality that is currently before the court.i Unfortunately, Muthana has become the poster case for the issue in the United States, and her situation has become part of the domestic partisan debate. U.S. actions in the Muthana case also seem to undermine President Trump’s call for other nations to repatriate their own nationals. Both the British and American cases are, however, exceptions, although the United Kingdom has stripped the citizenship of others. Revoking citizenship has limited applicability and limited effectiveness.

The majority of the United States’ jihadis who have been identified since 9/11 for involvement in terrorist attacks or plots in the United States or for traveling to jihadi fronts abroad48 (for whom citizenship information is available) are U.S.-born citizens whose citizenship is guaranteed by the Constitution and cannot be revoked. The same is true of those who traveled or attempted to travel from the United States to Syria.49 However, naturalized U.S. citizens can be stripped of their citizenship, leaving them with the citizenship of their country of origin. This is rare, but it has happened in the case of Nazi war criminals50 and some more recent terrorists.j

Stripping individuals of their citizenship works both ways. Countries that do so also abandon their ability to intervene if their former nationals end up being held under inhumane conditions, are being tortured, or face execution. It is easy to say that governments no longer have any responsibilities or concerns about the fate of its de-naturalized citizens, but it will require extraordinary sang-froid and impassivity to maintain resolve. One can easily envision future political scandals.

Turn them over to the Syrian or Iraqi government.
The Islamic State fought against the Syrian government and seized control of territory in Iraq. Therefore, either government may claim jurisdiction over the foreign volunteers who joined the Islamic State. They are guilty of crimes in both countries.

Iraq has offered to try the foreign Islamic State detainees, provided that members of the U.S.-led coalition reimburse it for the costs of the proceedings and detention. The estimated cost of the trials would be about $2 billion.51

Iraq has already tried and sentenced several hundred foreign Islamic State fighters, including a small number of Europeans.52 k France’s foreign minister, Jean-Yves Le Drian, stated in January 2019 that Islamic State fighters and their wives were enemies of France and should face justice in Syria or Iraq.53 Twelve nationals reportedly have been transferred from Syria to Iraq where they await trial.54

French policy, in fact, is more complex and has shifted over time. Since making his earlier statement, Le Drian has said that “we are exploring all options in order to prevent these potentially dangerous individuals from escaping or dispersing … If the forces detaining these French fighters decide to deport them to France, they would be immediately handed over to the judicial authorities.”55 In other words, they may return, but will face prosecution. However, in late March 2019, Le Drian said that French women who had joined the Islamic State would not be allowed back: “These women are ‘fighters’ and ‘should be treated as such’ … ‘there is no possibility for these women to be accepted back.’”56

Apart from the costs, the Iraqi offer raises a number of legal issues. Iraq has the death penalty, which Europe opposes. In one reported case, a European Islamic State member was sentenced to death in Iraq, but this was commuted to life in prison on appeal.57

And while the Iraqi constitution guarantees the right of a fair trial and prohibits torture or degrading treatment, the Iraqi justice system is considered weak and may not be able to ensure the necessary safeguards. Countries cannot always protect their citizens who are arbitrarily arrested or mistreated abroad, but can they actively participate in an arrangement that places their citizens at a lesser standard of justice and treatment? Would continued monitoring be required? Alternatively, can countries that strip Islamic State fighters of their citizenship still set conditions for the treatment of their ex-nationals? Possibly they could, if they obtain written guarantees and offer financial support in return. However, the European Court of Human Rights could intervene to prevent European countries from being complicit in schemes involving even those who are dual nationals being consigned to prisons in countries with poor human rights records.

Syria is a worse case. The Assad government has already been accused of war crimes and has a dismal record of mistreating prisoners.58 International humanitarian law prohibits repatriating detainees if they face torture, cruel, or degrading treatment. It seems that the same legal principle would apply to turning over prisoners to governments that are likely to mistreat them. One can also envision future domestic political scandals in countries whose nationals are held in Syrian dungeons.

Pay the Kurds to hold them indefinitely.
The SDF itself is an ad hoc paramilitary force. Its legal authority is not recognized internationally. Kurdish political authorities have expressed no interest in assuming responsibility for the captives. And in any case, there is no internationally recognized Kurdish state, and there is opposition to anything that might give them the trappings of sovereignty. Turkey would certainly oppose any arrangement that formalized international arrangements with the Kurds. As with Iraq and Syria, there is also the question of whether the contributing countries would thereby incur some responsibility for the conditions of captivity and ultimate fate of those held.

At best, this would seem to be an interim measure to buy time for the international community to produce a coordinated approach. However, it is easy to envision what is initially viewed as an ad hoc temporary measure, given continued international inaction, becoming a permanent feature of the landscape.

Individual countries agree to repatriate, investigate, and prosecute or monitor their own nationals.
This is the preferred policy of the United States and several European countries. Owing to existing laws, however, not all European countries may be able to successfully prosecute those who left to join the Islamic State. Under the material support provision, U.S. law prohibits even attempting to join a designated foreign terrorist organization. The United Kingdom has adopted a similar law. France may prosecute returning foreign fighters for participating in a group formed for the purpose of preparing an act of terrorism. But other countries lack such laws and argue that even if changed now, such a law cannot be made retroactive. Some require a formal declaration that it is forbidden to join a specific group in order to prosecute those who do so. Others require proof of actual participation in specific terrorist crimes such as kidnapping or murder. Evidence of such participation may be hard to come by. Prohibitions on the use of evidence gained through intelligence operations such as electronic surveillance further hinder prosecution in a number of European countries. Ordinary courtroom requirements are difficult to meet in conflict zones.

Analysts have offered different assessments of the likelihood that the fighters returning to Europe will engage in terrorist attacks at home after their return. Earlier estimates tend to be higher owing to the fact that the smaller population of jihadi travelers included many who went abroad specifically to obtain training for terrorist attacks at home. In the early days of the civil war, some traveled to Syria to provide humanitarian assistance and returned early as the conflict escalated, while others were swept up in the fighting and ended up in rebel formations. The number of Europeans traveling abroad to join the Islamic State (and other jihadi organizations) after 2012 increased sharply, but the exodus also included many who simply wanted to live in the caliphate created by the Islamic State. It is a very mixed population.

Although more than 1,700 have returned to Europe,l it may be too early to make a judgment about their intentions to bring the armed jihad home. Some of these went to Syria early in the conflict and returned early. In the United Kingdom, a significant proportion of these early travelers were by early 2019 assessed as no longer being of national security concern.59 m European intelligence service and law enforcement organizations have also intensified their activities to head off such attacks. On the other hand, the conditions that radicalized thousands of European nationals and residents have not fundamentally changed. Those who have returned disillusioned, determined to leave the Islamic State behind, will be under pressure from other extremists to rejoin.

The situation in the United States is very different. Of the 281 individuals identified by the author as having gone abroad to obtain terrorist training or fight in the ranks of a jihadi group, as already noted only one (the 2010 Times Square attempted bomber Faisal Shahzad) carried out an attack after his return. Two deadly terrorist attacks were carried out by individuals who spent time abroad that may have contributed to their radicalization—2009 Little Rock shooter Carlos Bledsoe and 2013 Boston bomber Tamerlan Tsarnaev—but they are not known to have connected with any terrorist group or received any terrorist training while abroad.

Ten percent of the total travelers from the United States participated in terrorist plots after their return, but as already mentioned, only one returnee from Syria was involved in a subsequent terrorist plot in the United States. The individual in question—Abdirahman Sheik Mohamud—served as a foreign fighter with the Jabhat al-Nusrah Front in 2014.60 n Almost all of the other returnees from Syria were arrested upon or shortly after their return.61

Even if convicted of terrorism-related crimes, jail sentences in Europe are short compared to the long sentences handed down in the United States, which many Europeans see as an appalling and undesirable form of oppression, and seldom do those convicted in Europe serve their full sentences. Jail time may only increase radicalization. Radicalization is a serious problem in European prisons.62 Jailed returning foreign fighters may intensify their own commitment and may radicalize others. Monitoring those at large and those who served time will pose an added burden on already stretched resources. Given the uncertainties and risks, few nations have formally accepted the transfer of their nationals from SDF custody.o Most of the returnees have made their own way back.

Utilize the International Criminal Court (ICC) or create a new international tribunal.
The Kurds have suggested the creation of an international tribunal under the auspices of the United Nations to sort out those currently held.63 Belgium has backed the idea, although with reservations.64 There are a number of complications. While there is ample international precedent for special tribunals—Nuremburg, Rwanda, Yugoslavia, and Iraq—these have dealt with those accused of war crimes—genocide, mass murder, ethnic cleansing, torture of prisoners. Although both the Islamic State and al-Qa`ida are considered by the United Nations to be terrorist organizations, merely joining the Islamic State or providing some measure of support may not by itself rise to the level of a war crime. Individual guilt may be required. The Special Tribunal for Lebanon, set up in 2009 following the assassination of Lebanon’s prime minister, addresses the crime of terrorism, which is significant because it is the only international tribunal established to deal expressly with acts of terrorism—the killing of the former prime minister of Lebanon.65 Therefore, it could be seen as a precedent for a tribunal to try those who fought for or supported the Islamic State without necessarily having to prove war crimes or crimes against humanity.

The international community conceivably could declare all members of designated terrorist organizations to be hostis generis humani—enemies of humanity—a designation applied to pirates on the high seas and slavers centuries ago. They stood outside the normal protections of the law and could be dealt with by any nation. The closest thing in the modern era was the continued hunt for and prosecution of Nazi war criminals down to the level of ordinary guards at concentration camps. (This would require a new international convention, which probably could not be done in time to affect the detainees in Syria.)

Beyond the legal question are the practical matters. The ICC deals with individual high-profile cases involving those responsible for mass atrocities. The leaders of the Islamic State could be brought before the ICC, but the ICC’s Prosecutor noted in 2015 that while it appeared that some foreign fighters had participated in crimes against humanity and war crimes, the Islamic State was led primarily by nationals of Iraq and Syria (neither of which is a party to the treaty creating the international court), and therefore the prospects of investigating and holding Islamic State foreign fighters accountable before the court were limited.66 The ICC would normally focus responsibility for war crimes on leadership rather than foot soldiers. Additionally, ICC prosecutions often take years to conduct, and institutionally, the Court has not prosecuted large numbers of people.

Moreover, not all nations support the ICC. The United States is not a member and in April 2019 revoked the visa of the ICC’s head prosecutor for even considering prosecuting American military personnel who served in Afghanistan for possible war crimes.67

The idea of an E.U. tribunal to deal with the European cases has come up for discussion. Sweden, for one, has broached the idea of an international or Europe-wide tribunal with the E.U. Council.68 The lack of consensus on the issue poses a political challenge. Not all European countries are supportive of repatriating those who went to join the Islamic State or live in the so-called caliphate it created. Bringing them back where they may immediately or eventually move freely across borders represents a threat to all. The opponents of repatriation may not be able to prevent individual countries from repatriating their own nationals, but can refuse to support a Europe-wide repatriation effort.

No international tribunal solves the problem of where to hold those convicted unless each nation agrees in advance to take and maintain custody of its nationals. But is it legitimate for nationals to be held in prisons in a country when they have not been tried in its own courts and under its own laws?

The United States steps in as the detainer of last resort and accepts custody.
The Islamic State remains a foreign terrorist organization under U.S. law. The United States led an international coalition to destroy the group. U.S. military forces are still deployed across Africa, the Middle East, and Asia, assisting local governments in their fight against the group and conducting special operations. U.S. intelligence officials consider the Islamic State to be a continuing terrorist threat. The United States has ample motive to ensure that those captured do not escape. The means are also there.

U.S. officials have said that foreign fighters who cannot be repatriated to their own countries could be brought to the U.S. military prison at Guantanamo Bay in Cuba where other foreign jihadis have been held since 2002. During his 2018 State of the Union address, President Trump asked Congress “to ensure that, in the fight against ISIS and al-Qaida, we continue to have all the necessary power to detain terrorists…And in many cases for them it will now be Guantanamo Bay.”69 More recently, four U.S. senators have urged President Trump to send Islamic State fighters currently detained in Syria to Guantánamo.70 The Pentagon’s spokeperson for Detainee Policy said “Guantánamo detention remains an alternative to repatriation of captives now held by the Syrian Democratic Forces.”71

Such a step undoubtedly would provoke protest among those concerned about violations of human rights, which Guantánamo has come to symbolize for many Europeans. (Whether the protest would be greater than if the detainees were instead turned over to serve time in Iraqi or Syrian prisons is not clear.)

The military tribunals at Guantánamo have been very slow; indeed, a number of their verdicts have been overturned by U.S. federal courts.p Although the April 2019 reversal of some tribunal decisionsq was based on the military judge’s undisclosed conflicts of interest, the prosecutions have been generally hampered by the fact that much of the evidence for prosecution has been obtained through what some call “enhanced interrogation techniques” and many regard as torture.72 r These defendants cannot get a fair trial, and they will not be released. There may be enough beds at Guantnamo, but adding even a small number of detainees to the 40 detainees73 who remain at Guantanamo would be politically difficult domestically and unacceptable internationally. It is difficult to imagine the United States taking custody of hundreds of foreign fighers. It would overwhelm the already sclerotic judicial process, increasing the likelihood of indefinite detention without prosecution and trial and destroying the image of justice served. And, as the United States has learned, once the United States accepts custody, it is extremely hard to persuade other countries to take back their nationals, some of whom may be stripped of their citizenship.74

U.S. law also allows the prosecution of foreign terrorists in regular U.S. courts, which would have greater international legitimacy. Presumably, this would involve only high-value detainees—leaders and those who participated in terrorist crimes against U.S. citizens abroad. Bringing to justice those who participated in the kidnapping and murder of U.S. citizens in Syria would be politically popular with some in the United States, but for a variety of reasons opposed by others who prefer they be sent to Guantánamo. The issue would undoubtedly be highly politicized.

Some U.S. legal experts have already advised against the United States assuming responsibility for prosecuting Islamic State detainees.75 An expression of such a willingness could reduce pressure on the European governments to repatriate and prosecute their own fighters.

Bluster and muddle.
This is not an option, but policy by default. It describes the current situation. Warnings and threats prompt concern, but international coordination remains too complicated. Each country does its own thing, with some stripping those who went to Syria of their citizenship while others promise prosecution, attempt rehabilitation, or ignore the problem.

The European Union has identified this as a priority issue and has introduced a package of legal measures to increase the capability of the European Union and individual members to deal with returning foreign fighters, but this is a slow process.76 Doing business as usual fails to recognize that these are special and urgent circumstances and it should not be tolerated. Inertia will prevail unless there is a major incident that highlights the danger or a humanitarian disaster that commands international attention.

The United States faces far smaller numbers of potential returnees and has wider latitude in prosecuting them. There may also be some high-profile individuals, either leaders or those who committed crimes against Americans, who the United States would want to bring back and prosecute.

Of particular interest to the United States, for example, is the prosecution of the two remaining so-called “Beatles”—a cell of four British foreign fighters involved in the torture and beheadings of Western hostages held by the Islamic State, including two American and two British hostages. One of the four was killed in a U.S. airstrike. Another was arrested and is in prison in Turkey. Two are currently detained by the SDF. The British government, which did not want to see the two men returned to the United Kingdom and stripped them of their citizenship, agreed to assist their prosecution in the United States by sharing evidence that it had collected about their actions. It did so without obtaining the usual guarantees that the two would not face execution or be sent to Guantánamo. The mother of one of the two challenged this arrangement in court, but her challenge was rejected in January 2019.77

No one obvious solution stands out and preferred solutions may not be feasible, but reviewing all the options does identify some non-starters and points to some paths forward. Simply letting the foreign fighters go is not an option. Allowing them to escape must be prevented. Stripping of citizenship is an inadequate and counterproductive response and, in any case, can be done in only a limited number of cases. Paying the Kurds to hold the detainees is a possible short-term measure, not a long-term solution. Turning them over wholesale to Syria and Iraq will create other problems. The International Criminal Court is not the right venue. The creation of a new international tribunal is a possibility not to be dismissed, but may be too complicated and would likely take too long to establish. For the same reasons, any formal multinational tribunal—for example, a European tribunal—seems unlikely. Most likely, the issue will be handled at the national level, which means different approaches will co-exist. That leaves some combination of repatriation, uncoordinated muddling, and potentially unilateral U.S. action aimed at the American and a few of the other identified detainees.

While messy, as most things are, this combination of approaches can be made to work. The first order of business is to inventory and disaggregate the populations. Foreign fighters can be sorted according to their role in the Islamic State, their desire to return, and their willingness to face prosecution or even confess to their crimes and assist the authorities. The same criteria apply to the women. The children should be rescued. The difficulty here will be an unrepentant mother with a small child. Separation may be inevitable in some cases, as it is when a child’s only parent is a convicted felon being sent to prison, but it cannot be a matter of policy. These decisions will have to be made on a case-by-case basis.

If international tribunals are too far a reach, putting together a multinational arrangement for screening should be possible. It can be done in the SDF-held territory under the auspices of the same governments that participated in the coalition’s campaign against the Islamic State and should be seen as a necessary component of their mission.

Sorting, Interviewing, Detention, and Prosecution
Sorting out the fighters and families for repatriation and prosecution and possible incarceration or rehabilitation and re-entry into society, and interviewing them for the purposes of intelligence collection or increasing our understanding of jihadi appeal, mindset, and networks are separate processes with different goals. The interviewing process should have several components, each with its own objectives.

The most difficult task will be to isolate the still dedicated jihadis. There will be no bright shining line here, but rather shades of commitment, which are fluid over time. In assessing the degree of ongoing commitment to the extremist cause, it may be necessary to discount some of the initial enthusiasm shown by the travelers when they were planning or first went to Syria. Some probably were disillusioned if not appalled by the harsh rule they saw compared to what they imagined when they first went. At the same time, those who simply accompanied spouses or other family members may have radicalized during their time in Syria or Iraq. Does a display of defiance on the part of some reflect continued jihadi sentiments or fear of possible Islamic State informers and enforcers still operating in the camps?

The willingness of the governments of the foreign fighters to accept risk will also be a variable. Recollections of past and recent terrorist attacks involving returnees will reinforce a natural tendency to err on the side of caution in repatriating nationals, which can amount to a lack of appetite for making distinctions.

Another component of this inquiry will be to assess the ability of home governments to prosecute individuals on the basis of available evidence. A number of Islamic State recruits extensively used social media, which means that there is an extensive amount of potentially self-incriminating material in social media before and during the time the travelers spent in Syria. However, fighters often used noms de guerre, and it may be difficult to legally connect cyber identities and posts with specific individuals.78 A parallel component will be intelligence collection, part of which will be aimed at gathering evidence that can be used in prosecution and at collecting intelligence about recruiting methods and routes that will facilitate shutting down future personnel pipelines.

In addition to this probative inquiry, the presence of hundreds of detainees and family members in one place will allow a broader interviewing process aimed at increasing understanding of the jihadi mindsets and subculture. This is voluntary and should not be seen as part of the legal investigation. An effort should be made to interview every single individual, not just those willing to talk, in order to prevent Islamic State spies and enforcers in the camps from easily identifying who might be cooperating simply by the length of time they spend with the interviewer. Other steps can be taken to create constructive ambiguity about this.

An initial assessment should be made to assess the resources required, number of trained interviewers, language skills, and physical infrastructure in a secure environment to process these individuals within a specified time period. These are interviews to sort out the population, not trials. Information collected during the screening process should be readily shared among the nations involved according to locally agreed upon rules, not elaborate intelligence-sharing protocols. At the same time, conditions should be improved in the camps. It will prevent unnecessary misery and potential humanitarian crises and improve the environment for interviewing. Security could be provided by the SDF, backed by coalition forces.

The objective of this screening would be to move people out of the camps and back to their countries of origin where they can be formally prosecuted or be reintegrated into society according to national plans in place. Getting the foreign fighters back and putting them in prison or placing them under some other type of controls will not remove them as a potential problem—terrorist threat or source of future radicalization.

De-radicalization and reintegration deserve more attention. Several European countries—Denmark, France, Germany, Netherlands, Sweden, the United Kingdom—have put in place prevention or de-radicalization programs, but the issues involved are more complicated than they had initially expected and they are still struggling to refine these efforts. Some approaches appear to have worked better than others. All are works in progress.79

Returnees from Syria are likely to be targets of societal rejection and potentially future revenge. Others may have suffered severe mental trauma that may hinder their ability to function normally in society.80 It is a long-term effort.

Any efforts to reinstate rather than lock up Islamic State returnees face exceptional hostility, especially in the current political climate in Europe and the United Sates. Recollections of Islamic State atrocities, fear of terrorism underscored by continuing attacks, Islamophobia, and growing anti-immigration sentiments will color how Western governments approach this issue. De-radicalization programs can easily become political footballs and entail political risks. That does not mean that Europe, North America, Australia, and others cannot develop programs that are suitable to their social and political environments.

With government commitment and community engagement, programs aimed at de-radicalization can help reduce—not eliminate—the risk of terrorist violence. The British have invested heavily in community-led preventive intervention and de-radicalization programs at the individual level and can claim a measure of success.81 The United Kingdom is implementing a “managed return” of those coming back from Syria. This includes the potential use of “Temporary Exclusion Orders” (in-country controls), criminal investigations, and rehabilitation and reintegration into society. An estimated 400 individuals have already come back.82

Everyone can agree that if the environment cannot be changed and the paths to violence cannot be interrupted, the production of jihadi terrorists will continue. The return of hundreds of Islamic State veterans, with no further intervention other than possible jail time, will only exacerbate the problem. Some type of de-radicalization program or other efforts to rehabilitate the returnees beyond incarceration are essential. It would be useful to know more about the life trajectories that drew the travelers to Syria to begin with, which brings this article back to researchable issues and the utility of conducting interviews while there is a ‘captive’ population in the camps.

It also may be useful to explore what tactical opportunities the returnees might provide. The counterterrorism community tends to focus exclusively on those who might still pose a threat, but given the numbers, there must also be some who may be turned into assets that can help discourage individuals from following their course. The administration of justice is important, but the objective is also resolving an armed struggle, and that requires thinking strategically and creatively to exploit opportunities offered by the current circumstances.

The territory occupied by the Islamic State in Iraq and Syria has been recovered, and as a consequence, a large number of Islamic State fighters, supporters, and family members have been detained. But the threat posed by the Islamic State continues. How can the current detainees be utilized as a resource in the continuing global struggle against the Islamic State, not just dealt with as a threat or burden? What are the risks of trying versus the risks of not trying?

Progress is being made. France and Belgium has done some interviewing of those seeking return.83 Some screening is also being done. The United States is helping countries put into place the laws and procedures seen as necessary to improve the prospects of prosecution.84 The biometrics of the detainees are being recorded,85 which will help prevent them from traveling internationally as border-control technology is being enhanced. The Radicalization Awareness Network, a European organization that includes practitioners across Europe, has produced a manual to assist governments and civil society on the “re-socialization” of returnees.86

But the efforts are disjointed, and progress appears to be slow. The SDF, with U.S. backing, recaptured Raqqa, the capital of the Islamic State in Syria, in October 2017. President Trump proclaimed the defeat of the Islamic State in December 2018 and ordered the withdrawal of all U.S. troops. Baghouz, the last town held by the Islamic State in Syria, fell in March 2019.

Defeating the Islamic State and recovering the territory it seized in 2014 is clearly a victory. It has been a more-than-four-year campaign, hard fought, costly in blood and treasure, immensely destructive as all wars are, with heavy casualties among civilians as well as fighters. The military effort has significantly reduced the terrorist threat. But that military achievement can easily be undone by failing to address what it has brought. Thousands of jihadis have been killed. Including fighters and active supporters, thousands of Islamic State fighters and families now remain in custody. While the challenge is considerable and the risks cannot be dismissed, those now detained must not be allowed to become the next generation of terrorists by failing to reintegrate them or remove them from society.     CTC

Brian Michael Jenkins is a former soldier and currently serves as Senior Advisor to the President of the RAND Corporation, where he initiated one the nation’s first research programs on terrorism in 1972. His books and monographs on terrorism include International Terrorism: A New Mode of Conflict Aviation; Terrorism and Security; Unconquerable Nation; Will Terrorists Go Nuclear?; The Long Shadow of 9/11; When Armies Divide; and The Origin of America’s Jihadists.

The views expressed in this article are solely those of the author and do not necessarily reflect the perspectives of the Combating Terrorism Center, the United States Military Academy, or RAND.

Substantive Notes
[a] All of the totals in the ICSR study include women and minors, the principal focus of the report. However, between 2013 and 2018, an unknown number of minors were born to foreign travelers living in Islamic State-controlled territory. Ibid.

[b] The 281 comprise U.S. persons who were arrested between 9/11 and October 2018 for traveling or attempting to travel abroad to join any known jihadi organization. A few had traveled to Afghanistan as early as the 1980s to participate in the resistance against the Soviet invasion; they were arrested after 9/11 for participation in terrorist plots.

[c] The majority of terrorist plots and attacks in the United States involve a single perpetrator. Brian Michael Jenkins, “Middle East Turmoil and the Continuing Terrorist Threat–Still No Easy Solutions,” Testimony before the Committee on Armed Services of the United States House of Representatives, February 14, 2017. See also Brian Michael Jenkins, The Origins of America’s Jihadists (Santa Monica, CA: The RAND Corporation, 2017).

[d] There were extensive interviewing efforts focusing on German fighters and civilians during and immediately after World War II. During the Vietnam War, the RAND Corporation conducted approximately 2,400 interviews with captured Viet Cong and North Vietnamese prisoners, defectors who voluntarily left the Viet Cong or North Vietnamese army, refugees from battle areas, and others familiar with the operations of the Viet Cong and North Vietnamese forces. Putting aside the understandable and widespread opposition to the Vietnam War and the ultimate failure of American efforts in South Vietnam, the reports of those interviews offered an extraordinarily rich source of information about the political and military upheaval, the Viet Cong and North Vietnamese army, and Vietnamese rural life. In the author’s view, had closer attention been paid to this material, it would have altered U.S. political expectations and its military strategy. The point in mentioning the study here is certainly not to awaken old controversies or advertise the Vietnam War as an example to be emulated, but rather to indicate that large-scale, in-depth interviewing—not just interrogations to obtain operational intelligence or brief interviews to assess threat or prosecution potential—can lead to a deeper understanding of a still-formidable adversary and, in particular, of the process by which thousands of young men and women join an enterprise that not only exhorts violence, but advertises its atrocities. Projects aimed at interviewing terrorists have been few and modest in scope, but nonetheless produced valuable, policy-relevant insights.

[e] There have been reports that some women in the camps are “being threatened by more militant Russian and North African wives of ISIS fighters, who they said were trying to enforce ISIS rules within the camp.” Jane Arraf, “Misery Grows At Syrian Camp Holding ISIS Family Members,” NPR, May 23, 2019.

[f] The latest map of Iraq prepared by the Institute for the Study of War shows isolated pockets of continuing attacks by the Islamic State and significant zones of support in northern and western Iraq and in southern and eastern Syria. “ISIS Operating Areas: April 16, 2019,” Institute for the Study of War.

[g] However, according to article 132 of the Fourth Geneva Convention, “the Parties to the conflict shall, moreover, endeavour during the course of hostilities, to conclude agreements for the release, the repatriation, the return to places of residence or the accommodation in a neutral country of certain classes of internees, in particular children, pregnant women and mothers with infants and young children, wounded and sick, and internees who have been detained for a long time.”

[h] In December 2018, President Trump announced that all U.S. forces would be withdrawn from Syria, a decision that reportedly prompted Defense Secretary James Mattis to resign. However, in February 2019, the White House announced that 200 troops would remain. Dion Nissenbaum and Nancy A. Youssef, “U.S. Military Now Planning to Leave as Many as 1,000 Troops in Syria,” Wall Street Journal, March 17, 2019. On March 17, 2019, The Wall Street Journal quoted U.S. officials who said that up to 1,000 troops might stay in Syria. Chairman of the Joint Chiefs of Staff General Joseph Dunford denied the report that the February planned drawdown had changed, but add that planning continued. “U.S. denies plans to leave 1,000 troops in Syria,” Defense Post, March 18, 2019.

[i] Lawyers representing Muthana have disputed her father’s status at the time of her birth; she had been issued a U.S. passport twice. Jonathan Shaub, “Hoda Muthana and Shamima Begum: Citizenship and Expatriation in the U.S. and U.K.,” Lawfare, February 25, 2019.

[j] In April 2019, a naturalized U.S. citizen was stripped of his citizenship for concealing his previous conviction in Israel for participation in a terrorist attack. “Man convicted of bombing Israeli bus loses U.S. citizenship,” Associated Press, April 26, 2019. In 2017, the U.S. Department of Justice sought to revoke the citizenship of Iyman Faris, an al-Qa`ida operative convicted in 2003 of plotting to destroy the Brooklyn Bridge. The Justice Department claimed that Faris made false statements when he applied for citizenship. Robert Chesney, “DOJ Sues to Revoke the Citizenship of Convicted al Qaeda Operative Iyman Faris (A Naturalized Citizen),” Lawfare, March 20, 2017. In July 2018, a federal judge ruled against the government. “Judge rejects US efforts to strip citizenship from terrorist jailed in Illinois,” Associated Press, July 21, 2018. The case continues while Faris completes his prison term. Since 9/11, there have been a number of bills introduced into Congress aimed at stripping terrorists of their citizenship. James H. Martin, “Terrorism-Related Loss of Citizenship–A Policy Review,” master’s thesis, Naval Postgraduate School, Monterey, California, September 2016.

[k] Twelve French nationals and at least one German national were turned over to the Iraqi authorities, reportedly with the agreement of the home countries.

[l] According to Europol, approximately 5,000 individuals from the European Union were believed to have traveled to conflict zones in Syria and Iraq. By late 2017, it was thought that about 1,500 had returned home; 1,000 were believed to have been killed. “TESAT-2018: European Union Terrorism Situation and Trend Report,” Europol, 2018.

[m] For example, approximately 400 UK citizens who traveled to Syria have returned. Approximately 10 percent have been prosecuted. “UK Nationals Returning from Syria,” They Work for You, UK House of Commons, All Commons debates on 18 February 2019.

[n] Abdirahman Mohamud traveled to Syria in 2014 where he trained with and briefly fought as a member of Jabhat al-Nusrah, al-Qa`ida’s affiliate in Syria. He returned to the United States in June 2014, shortly after his brother, also a jihadi foreign fighter, was killed. He planned to obtain weapons to carry out attacks on military officers and other government officials, but was arrested by the FBI before he was able to develop his plans.

[o] Kosovo accepted the return of 110 fighters and family members transferred with U.S. assistance from Syria. Fatos Bytyci, “Kosovo brings back fighters, families of jihadists from Syria,” Reuters, April 19, 2019. Reportedly, a few Dutch foreign fighters have returned with the government’s help. Bruce Bawer, “Dealing with Europe’s ISIS Returnees,” FrontPage, February 20, 2019. France has recently announced that it will repatriate French jihadis currently detained in Syrian camps. James McAuley and Michael Birnbaum, “France to take back ISIS fighters, reversing policy in wake of U.S. withdrawal from Syria,” Washington Post, February 1, 2019.

[p] In 2012, the U.S. Supreme Court overturned the conviction of one detainee on the grounds that the crime for which he was convicted was not a crime at the time of his alleged conduct. See Josh Gerstein, “Court overturns conviction of bin Laden driver,” Politico, October 16, 2012. In April 2019, a federal appeals court overturned the conviction of the alleged mastermind of the USS Cole bombing in 2000 on the grounds that the judge in the case had disclosed that he was seeking a job in the federal government while presiding over the trial, thereby creating a “disqualifying impression of partiality.” Missy Ryan, “In a setback for Guantanamo, court throws out years of rulings in USS Cole case,” Washington Post, April 16, 2019.

[q] The U.S. Court of Appeals for the District of Columbia overturned two years of decisions by the military tribunal judge presiding over the proceedings in the USS Cole bombing case. Charles Gallmaeter, “Federal appeals court vacates more than two years of decisions by military judge overseeing the USS Cole bombing case,” Jurist, April 17, 2019.

[r] Of the 780 detainees known to have been held at Guantanamo, 731 were released without charges, nine died while in custody, 41 remain in custody, including eight who were convicted by the military commissions. Three of these convictions have been overturned and three more partially invalidated, leaving a total of two convictions that have stood.

[1] “‘Foreign children’ in overwhelmed Syrian camp need urgent international help, says top UN official,” UN News, April 18, 2019.

[2] Ibid.

[3] Ben Hubbard, “In a Crowded Syrian Tent Camp, the Women and Children of ISIS Wait in Limbo,” New York Times, March 29, 2019.

[4] Jalal Zainedine, “Where are ISIS Fighters Following Its Military Defeat?” Chatham House: The Royal Institute of International Affairs, November 2018.

[5] “How many IS foreign fighters are left in Iraq and Syria,” BBC, February 20, 2019.

[6] Natan Sachs, Nathan Sales, and Daniel Byman, “After the Caliphate: A Global Approach to Defeating ISIS,” Brookings Institution, April 30, 2019.

[7] Nancy A. Youssef and Gordon Lubold, “U.S.-Backed Forces Are Holding 2,000 Suspected ISIS Fighters in Syria,” Wall Street Journal, March 5, 2019; Ryan Browne and Jennifer Hansler, “US officials say more than 2,000 suspected foreign ISIS fighters being held in Syria,” CNN, April 17, 2019.

[8] Hubbard.

[9] A vivid description of conditions in the SDF temporary prisons and the complex attitudes of the detainees is provided in Robin Wright, “The Dangerous Dregs of ISIS,” New Yorker, April 16, 2019.

[10] “U.S. Expects Every Country to Take Back Foreign Fighters: Pompeo,” Reuters, May 8, 2019.

[11] “Shamima Begum: IS teen’s return to UK ‘could be prevented,” BBC, February 15, 2019.

[12] Rowena Mason, “Trump is right, UK must take back ISIS fighters–ex-British army chief,” Guardian, February 17, 2019.

[13] Author interviews, personal conversations, and correspondence, European and NATO officials in Europe, March-April 2019.

[14] The author would like to thank Richard C. Daddario, Karen J. Greenberg, and Daphne Richemond-Barak for their helpful comments, especially on matters of law, and David A. Lubarsky for his careful and thoughtful review.

[15] Daved Gartenstein-Ross, Vivian Hagerty, and Logan MacNair, “The Emigrant Sisters Return: The Growing Role of the Islamic State’s Women,” War on the Rocks, April 2, 2018.

[16] Robin Simcox, “The 2016 French Female Attack Cell: A Case Study,” CTC Sentinel 11:6 (2018).

[17] Nadia Khomami, “How London teenager plotted attacks with all-female terror cell,” Guardian, June 4, 2018.

[18] Colleen McCue, Joseph T. Massengill, Dorothy Milbrandt, John Gaughan, and Meghan Cumpston, “The Islamic State Long Game: A Tripartite Analysis of Youth Radicalization and Indoctrination,” CTC Sentinel 10:8 (2017).

[19] “In an Islamic State training camp, children told: Behead the doll,” Chicago Tribune, July 19, 2015; Omar Abdullah, “ISIS Teaches Children How to Behead in Training Camps,” ABC News, September 6, 2014.

[20] “Dozens of Regime Forces Killed in ISIS Attacks in Syria,” Asharq al-Awsat, April 20, 2019.

[21] Suadad al-Salhy, “Al Qaeda says it freed 500 inmates in Iraq jail-break,” Reuters, July 23, 2013. Although the headline says “al Qaeda,” the group that carried out the jail-break was the Islamic State, then still an al-Qa`ida affiliate. See also Aki Peritz, “The Great Iraqi Jail Break,” Foreign Policy, June 28, 2014.

[22] Peter Salisbury, “Al-Qaeda militants free as many as 300 in Yemen prison break,” Financial Times, April 2, 2015.

[23] Joana Cook and Gina Vale, From Daesh to ‘Diaspora’: Tracing the Women and Minors of the Islamic State (London: International Centre for the Study of Radicalization, 2018). Although it is difficult to obtain reliable figures, the number cited by Cook and Vale is close to the “40,000 plus” figure offered in the most recent United Nations Monitoring Team report: “Twenty-Third Report of the Analytical Support and Sanctions Monitoring Team … concerning ISIL (Da’esh), Al-Qaida and associated individuals, groups, undertakings and entities,” United Nations, December 27, 2018.

[24] Brian Michael Jenkins, A Group Portrait of America’s Jihadists, Part Two: Comparing Jihadist Travelers Going Abroad with Domestic Plotters (Santa Monica, CA: The RAND Corporation, forthcoming).

[25] Cook and Vale.

[26] “Seventh report of the Secretary-General on the threat posed by ISIL (Da’esh) to international peace and security and the range of United Nations efforts in support of Member States in countering the threat,” United Nations Security Council, August 16, 2018, p. 6.

[27] Paul Cruickshank, “A View from the CT Foxhole: Edmund Fitton-Brown, Coordinator, ISIL (Daesh)/ Al-Qaida/Taliban Monitoring Team, United Nations” CTC Sentinel 12:4 (2019).

[28] Thomas Hegghammer, “The Rise of Muslim Foreign Fighters: Islam and the Globalization of Jihad,” International Security 35:3 (Winter 2010/2011): pp. 53-94; Thomas Hegghammer, “Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice Between Domestic and Foreign Fighting,” American Political Science Review (February 2013): pp. 1-15. See also Brian Michael Jenkins, When Jihadis Come Marching Home: The Terrorist Threat Posed by Westerners Returning from Syria and Iraq (Santa Monica, CA: The RAND Corporation, 2014).

[29] Jeanine de Roy van Zuijdewijn, “Fearing the Western Foreign Fighter: The Connection Between Fighting the Defensive Jihad and Terrorist Activity in the West,” master’s thesis, University of Utrecht, the Netherlands, January 2014.

[30] Ibid.

[31] Ibid.

[32] Jenkins, A Group Portrait of America’s Jihadists.

[33] Ibid.

[34] Brian Michael Jenkins and Jean-Francois Clair, Trains, Concert Halls, Airports, and Restaurants—All Soft Targets: What the Terrorist Campaign in France and Belgium Tells Us about the Future of Jihadist Terrorism in Europe (San Jose, CA: Mineta Transportation Institute, 2016). See also Jean-Charles Brisard and Kevin Jackson, “The Islamic State’s External Operations and the French-Belgian Nexus,” CTC Sentinel 9:11 (2016).

[35] Ibid.

[36] “Twenty-Third Report of the Analytical Support and Sanctions Monitoring Team,” pp. 13-14.

[37] Niharika Mandhano, Rob Taylor, and Saeed Shah, “Sri Lanka Bomber Trained in Syria with Islamic State,” Wall Street Journal, April 29, 2019. See also Sudha Ramachandran, “Sri Lankan Suicide Bombings: Islamic State’s Deadly Input,” Terrorism Monitor 17:9 (2019) citing an unnamed senior Sri Lankan police official.

[38] An excellent paper published in March 2019, after work on this essay began, looked at five options. This discussion examines eight. See Tanya Mehra and Christophe Paulussen, The Repatriation of Foreign Fighters and Their Families: Options, Obligations, Morality and Long-Term Thinking, International Centre for Counter-Terrorism, The Hague, March 6, 2019.

[39] Convention (IV) relative to the Protection of Civilian Persons in Time of War, Geneva, August 12, 1949, articles 132 and 133.

[40] Charles Lister, “Trump Says ISIS Is Defeated. Reality Says Otherwise,” Politico, March 18, 2019.

[41] Donald J. Trump, “The United States is asking Britain, France, Germany and other European allies to take back over 800 ISIS fighters that we captured in Syria and put them on trial. The Caliphate is ready to fall. The alternative is not a good one in that we will be forces to release them,” Twitter, February 16, 2019.

[42] Zaheena Rasheed and Farad Najjar, “Burden of victory: What should happen to European ISIL prisoners?” Al Jazeera, February 18, 2019.

[43] Corey Dickstein, “Votel: No timeline for U.S. troop withdrawal from Syria as ISIS caliphate nears end,” Stars and Stripes, March 7, 2019.

[44] The author is indebted to Daphne Richemond-Barak for the thoughts in this paragraph. Author correspondence, February 2019.

[45] “Shamima Begum: IS teenager’s baby son has died, SDF confirms,” BBC, March 8, 2019.

[46] Kevin Rawlinson and Vikram Dodd, “Shmina Begum: ISIS Briton faces move to revoke citizenship,” Guardian, February 19, 2019.

[47] Dara Lind, “The fight over whether ISIS recruit Hoda Muthana is a US citizen explained,” Vox, February 22, 2019.

[48] Brian Michael Jenkins, The Origins of America’s Jihadists (Santa Monica, CA: The RAND Corporation, 2017).

[49] Jenkins, A Group Portrait of America’s Jihadists.

[50] As one example of numerous cases, see “Detroit-Area Man Who Shot Jews While Serving as Nazi Policeman Ordered Removed from the United States,” Justice News, U.S. Department of Justice, February 9, 2011.

[51] “Iraq offers to try ISIS adherents if coalition pays millions in court costs,” Defense Post, April 10, 2019.

[52] Josie Ensor, “Iraq offers to try ISIL prisoners held in Syria for multi-billion pound fee,” Telegraph, April 10, 2019.

[53] Richard Lough and Caroline Pailliez, “France snubs Trump’s appeal to repatriate IS fighters en masse, for now,” Reuters, February 18, 2019.

[54] Ensor.

[55] James McAuley and Michael Birnbaum, “France to take back ISIS fighters, reversing policy in wake of U.S. withdrawal from Syria,” Washington Post, February 1, 2019.

[56] “French Foreign Minister: DAESH women will not be allowed back,” ANF News, April 1, 2019.

[57] “German ‘IS’ jihadi spared death sentence in Iraq,” Deutsche Welle, April 24, 2018.

[58] “Syria war: Lawyers submit first war crimes cases against Assad,” BBC, March 7, 2019. See also Anne Barnard, “Inside Syria’s Secret Torture Prisons: How Bashar al-Assad Crushed Dissent,” New York Times, May 11, 2019.

[59] “Shamima Begum: How do countries deal with people returning from IS?” BBC, February 15, 2019.

[60] “Columbus Man Sentenced for Providing Material Support to Terrorists, Making False Statements to Authorities,” United States Attorney’s Office: Southern District of Ohio, U.S. Department of Justice, January 22, 2018.

[61] Jenkins, A Group Portrait of America’s Jihadists.

[62] “Twenty-Third Report of the Analytical Support and Sanctions Monitoring Team.”

[63] Sarah El Deeb, “U.S.-backed Kurds want international tribunal for ISIS detainees,” Military Times, March 25, 2019.

[64] Wladimir van Wilgenburg, “Belgian government supports international prosecution for ISIS fighters,” Kurdistan24, February 21, 2019.

[65] The author is grateful to Daphne Richemond-Barak for drawing his attention to this and other legal precedents.

[66] “Statement of the Prosecutor of the International Criminal Court, Fatou Bensouda, on the alleged crimes committed by ISIS,” International Criminal Court website, April 8, 2015. See also Katherine Brown, “Returning Foreign Fighters–what are the ethical and practical responsibilities,” University of Birmingham website, July 2018.

[67] Marlise Simons and Megan Specia, “U.S. Revokes Visa of I.C.C. Pursuing Afghan War Crimes,” New York Times, April 5, 2019.

[68] Rachel Kennedy, “What is Europe’s approach to repatriating ISIS members? Euronews answers,” Euronews, March 7, 2019. See also “Sweden calls for international tribunal to bring ISIS fighters to justice,” Local (Sweden’s news in English), March 7, 2019.

[69] Scott Neuman, “Trump Signs Order to Keep Prison at Guantanamo Bay Open,” NPR: The Two-Way, January 31, 2018.

[70] “Senators Urge President Trump to Send ISIS Fighters to Guantanamo Bay,” press release from the Office of Tom Cotton, January 22, 2019.

[71] Carol Rosenberg, “U.S.: Guantanamo still an option for ISIS captives in Syria who can’t go home,” McClatchy, February 6, 2019.

[72] “Guantanamo by the Numbers,” Human Rights First, October 10, 2018.

[73] Ibid.

[74] Arun Rath, “Trump Inherits Guantanamo’s Remaining Detainees,” NPR, January 19, 2017.

[75] Benjamin R. Farley, “Shifted Burdens: The U.S. as Detainer of Last Resort,” Just Security, February 26, 2019.

[76] “The return of foreign fighters to EU soil: Ex-post evaluation,” European Parliamentary Research Service, May 2018.

[77] Adam Forrest, “High Court rejects challenge over UK sharing evidence about suspected Isis ‘Beatles’ terrorists with US,” Independent, January 18, 2019.

[78] Paul Cruickshank, “A View from the CT Foxhole: Peter Edge, ICE Acting Deputy Director, and Wil van Gemert, Europol Deputy Director,” CTC Sentinel 10:1 (2017).

[79] For a comparative survey of de-radicalization programs, see Rohan Gunaratna and Sabariah Hussin eds., Deradicalisation and Terrorist Rehabilitation: A Framework for Policy-Making and Implementation (Abingdon, U.K.: Routledge, 2018) and Rohan Gunaratna and Sabariah Hussin, International Case Studies of Terrorist Rehabilitation (Abingdon, U.K.: Routledge, 2018).

[80] Sabariah Binte Mohamed Hussin, “Deradicalisation and Rehabilitation: Way Forward for Returnees,” RSIS Commentaries, April 8, 2019.

[81] Paul Cruickshank, “An Interview with: Usman Raja,” CTC Sentinel 8:7 (2015); Paul Cruickshank, “A View from the CT Foxhole: Dr. Angela Misra, Co-Founder, The Unity Initiative,” CTC Sentinel 10:10 (2017); Paul Cruickshank, “A View from the CT Foxhole: Shaun Greenough, Case Strategy and Mentor Supervisor, The Unity Initiative,” CTC Sentinel 12:2 (2019).

[82] Rumyana van Ark, British Citizenship Revoked, Bangladeshi Citizenship Uncertain–What Next for Shamima Begum (The Hague: International Centre for Counter-Terrorism, March 11, 2019).

[83] Kennedy.

[84] Nathan A. Sales, Acting Under Secretary for Civilian Security, Democracy, and Human Rights, “After the Caliphate: A New Global Approach To Defeating ISIS,” U.S. Department of State, April 30, 2019.

[85] Seth J. Frantzman, “9,000 ISIS Fighters and 60,000 Family Members Held in Syria–Report,” Jerusalem Post, April 18, 2019.

[86] Marije Meines, Merel Molenkamp, Omar Ramadan, and Magnus Ranstorp, RAN Manual—Responses to returnees: Foreign Terrorist fighters and their families (Brussels: Radicalization Awareness Network, July 2017).

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