(Editor’s Note: This is the final of a two-part series on international legal obligations related to repatriating the thousands of foreign fighters who fought on behalf of ISIS in Syria. The first installment considered international law on the question. This part examines how to strengthen political will to address repatriations.)

The first of this two-part series highlighted the phalanx of United Nations Security Council Resolutions (UNSCRs) that impose obligations on member States to make their “best efforts” to investigate, repatriate, and take all lawful measures to ensure their nationals detained in the custody of the non-state armed group the Syrian Democratic Forces (SDF) do not return to the battlefield or engage in further terrorist activity. Given those international obligations, it is worth considering what is driving the political resistance to repatriation and what might be done to counteract such resistance.

A few impediments immediately come to mind: the lack of the necessary legal institutions for effective investigation, prosecution, and incarceration; a lack of effective programs for reintegration and rehabilitation of persons for whom criminal prosecutions are not appropriate (such as some returning family members); and a paucity of sufficient information or evidence to support criminal prosecutions and/or a range of other activity designed to prevent returning foreign terrorist fighters and their families from engaging in terrorist activity.

Stronger Institutions and Better Laws

At least some of the political resistance comes from the fear that the laws and institutions of the countries in question are inadequate to address the threat posed by a repatriated foreign terrorist fighter. As Washington Post columnist David Ignatius has noted, “Europeans protest that they don’t have adequate laws to try their nationals who committed terrorist offenses on foreign soil, and that they don’t have evidence that would stand up in court. They worry, too, that Islamist extremists in European prisons would radicalize other Muslim prisoners and then be released back into society in a few years, perhaps to commit new terrorist acts.”

Such concerns are, of course, shared by countries outside of Europe with far more profound legal, institutional, and resource-related challenges. Many countries to which foreign terrorist fighters must be repatriated suffer from institutional frailty and a lack of resources – factors that not only leave such countries vulnerable to attack, but also undermine confidence in the ability of judicial institutions to effectively incapacitate repatriated fighters and which, in turn, drives political reluctance to accept terrorists into their custody.

In order to address these concerns, and to ensure countries from which such terrorists emanate have the ability to effectively investigate and prosecute them, those governments will need to further develop their legal frameworks and their judicial capacity. For these reasons (and others), the 2018 U.S. National Strategy for Counterterrorism prioritizes building the capacity of partners’ judicial and law enforcement personnel and institutions:

We will continue to augment the capabilities of key foreign partners to conduct critical counterterrorism activities. We will help to professionalize the military, law enforcement, judicial, intelligence, and security services, as well as financial authorities, of key partners so that they are able to conduct counterterrorism operations effectively and justly. We will also work to ensure that partners meet their responsibilities in holding their citizens accountable for any acts of terrorism committed abroad.

Such efforts will also need to focus on the sentencing regimes in those countries where terrorists might be prosecuted and imprisoned. For instance, weak sentencing regimes in certain European countries have been cited by experts as being problematic:

In many European jurisdictions, the sentences available for those convicted of membership of terrorist organisations are limited to a few years’ imprisonment. The average sentence in Belgium for returned foreign fighters has been five years in jail. In July 2019, a German woman who had married an ISIS fighter was sentenced to five years’ imprisonment for joining a foreign terrorist organisation. The recent average sentence in the UK for membership of a terrorist group has been seven years. France stands out among EU member states for imposing relatively long sentences for the crime of “association of wrongdoing in relation to a terrorist enterprise[.]”

If a country cannot detain a convicted foreign fighter for more than a few years, then the political will of that country’s leaders to accept repatriation of such a terrorist will obviously be limited. No official wants to take responsibility for bringing back a terrorist only to have that person walking the street a few short years (or sooner) after his or her repatriation. This means that, in addition to supporting judicial capacity building to ensure international partners have the ability to properly investigate and prosecute terrorists, security imperatives dictate that European countries and other international partners must revisit their sentencing regimes and – in a manner that comports with international legal obligations and the rule of law – undertake efforts to impose longer sentences on returning fighters so that such terrorists can be incapacitated and do not pose a post-repatriation threat to national security.

Some action is already happening in this space. For instance, the United Kingdom recently introduced new emergency legislation, the “Terrorist Offenders (Restriction of Early Release) Bill,” which seeks to end the practice of releasing convicted terrorists halfway through their adjudged sentences in the United Kingdom. The measure was in response to an attack by a convicted terrorist who had been released from jail after serving half of his sentence and who had been under surveillance for roughly 10 days before stabbing two victims as part of a terrorist attack in south London.

According to a U.K. government fact sheet explaining the legislation, its aim is to “ensure terrorist offenders are not automatically released before the end of their sentence (or custodial term);” to “standardise the first eligible release point for offenders who have committed a relevant terrorist offence or an offence with a terrorist connection to the two-thirds point of their sentence;” and to introduce “a requirement for the release of all such offenders before the end of their sentence (or custodial term) to be decided by the Parole Board based on an assessment of risk.”

The attention given to this topic by the United Kingdom is promising and will hopefully catalyze additional, similar efforts by European countries and others.  If the officials and citizens of these countries can have faith that their institutions and legal frameworks can adequately protect them, then they may feel more confident in their ability to live up to their international legal obligations to “ensure appropriate prosecution, rehabilitation, and reintegration of FTFs and their accompanying family members.”  Accordingly, such judicial capacity-building and sentencing reform remains vital.

Supporting Terrorism Prevention and Countering Violent Extremism Programs

It is also worth noting that there are a range of other disposition options beyond prosecutions and incarceration. These options include intervention, rehabilitation, and reintegration efforts that seek to ensure that returning foreign terrorist fighters and their families – some of whom may not merit prosecution and incarceration – give up terrorist activity and are able to eventually reintegrate into society. Although the efficacy of such programs remains a topic of some debate (especially in the wake of the Usman Khan attack) there is general consensus in the national security community that such non-law enforcement means to address the threat of terrorism should be strengthened and sustained. For this reason, the 2018 National Strategy for Counterterrorism makes the support for such programs (intervention efforts, measures to limit prison radicalization, reintegration initiatives, etc.) a strategic priority.

Information-Sharing and the Use of Battlefield Evidence

Other key counterterrorism efforts involve information-sharing, especially the collection and sharing of “captured enemy material” or “battlefield evidence” among international partners. As U.S. Ambassador Nathan A. Sales, the State Department’s coordinator for counterterrorism, has noted, “Battlefield evidence is critical to a broad range of national security priorities. The United States and our partners can use this information to investigate and prosecute foreign terrorist fighters, screen and watchlist terrorist suspects, and protect our borders.”  For this reason, the 2018 U.S. National Strategy for Counterterrorism emphasizes the effective use and sharing of such information.

The United States and international institutions have undertaken an array of efforts to advance this concept. For instance, the U.S. State Department — in partnership with the Department of Justice, the Department of Defense, and others — has convened several “senior leaders seminars” and other events to discuss “the use of evidence gathered by military personnel following terrorist attacks in conflict zones in civilian criminal justice proceedings and other civilian counterterrorism missions.”

In addition, key international organizations such as the U.N. Counter-Terrorism Committee Executive Directorate (CTED) and the International Institute for Justice and the Rule of Law (IIJ) have developed guidelines on the effective use of battlefield evidence to help guide countries seeking to use such material for purposes of investigation and prosecution. The State Department has long supported the Commission for International Justice and Accountability, a non-profit that has worked to exfiltrate documents seized in Syria for the purpose of supporting national (and international) prosecutions.  In addition, pursuant to UNSCR 2379 (2017), an independent investigative team – the United Nations Investigative Team to Promote Accountability for Crimes Committed by Da’esh/ISIL (UNITAD) – has engaged in important work under UN auspices to support the domestic efforts of States to hold ISIS accountable for its terrorist activity.

Notably, one of the most innovative, cutting-edge, and institutionally developed multilateral platforms in existence for this kind of collaboration is the DOD-led initiative called “Operation Gallant Phoenix.” This multilateral platform provides a uniquely broad information and intelligence-sharing network across approximately 30 countries to assist in tracking the travel of foreign terrorist fighters and to ensure participating countries have information and evidence that permit successful investigations, prosecutions, or other actions to ensure such threats are neutralized. According to U.S. Marine Corps General Joseph Dunford, a former chairman of the Joint Chiefs of Staff, “It allows nations to collaborate and share information and be able to get it back to law enforcement to deal with the foreign fighter challenges.”

Combined with more routine, institutionalized forms of information-sharing, such targeted efforts can help ensure that countries to which foreign fighters are repatriated have the evidence needed for fulsome investigations, successful prosecutions, and effective border screening. In addition, having this information/evidence available may also make international partners more inclined to pursue repatriation as they will have greater assurances of an effective disposition option in their own courts.


Battlefield detention by non-state groups is increasingly common and has been recently brought into focus by events in Syria where, as part of the international effort to counter ISIS, the United States and coalition partners have worked “by, with, and through” a non-state armed group. This approach, however, has created a detention conundrum: States rely on non-state groups for counterterrorism operations, but they are simultaneously reluctant to accept the return of terrorists captured and detained by those partners in the course of operations.

Specifically in Syria, SDF partners have signaled that they do not have the capacity or authority to continue detaining captured foreign fighters. At the same time, the countries of origin of these fighters cite a range of legal obstacles to accept their return. The combination risks the release of dangerous individuals.

But international law requires States to make “best efforts” to bring foreign terrorist fighters to justice. That means the transfer of foreign fighters from the custody of a non-state entity to government authorities for prosecution, rehabilitation, or other appropriate means of preventing their return to terrorism. States that lack that political will to do so must take a hard look at their legal regimes and institutions and make the reforms needed so that they can effectively live up to their international legal obligations. As U.S. Marine Corps General Kenneth F. McKenzie, commander of U.S. Central Command (CENTCOM), has emphasized, “This problem will not go away by ignoring it, and can only be addressed by the international community working together to accept its shared responsibilities.”

IMAGE: A fighter with the Syrian Democratic Forces (SDF) monitors on surveillance screens, prisoners who are accused of being affiliated with the Islamic State (IS) group, at a prison in the northeastern Syrian city of Hasakeh on Oct. 26, 2019. Kurdish sources said around 12,000 IS fighters including Syrians, Iraqis as well as foreigners from 54 countries were being held in Kurdish-run prisons in northern Syria. (Photo  FADEL SENNA/AFP via Getty Images)