The question of what to do with Western Muslims who joined Daesh returned to the news last week, as the London Times’ premier war correspondent, Anthony Loyd, produced another report from the Kurdish prison camps in Syria where many are being held. Packed into cells so tightly that they were unable to move without touching someone else, the European and American prisoners that he spoke to asked to come home. At Al-Hol camp, where Daesh women and children are held, the group’s rules still hold sway and those who break them are murdered. Their Kurdish jailers fear a Daesh attack on the prison, freeing the inmates to rejoin its murderous ranks. Most Western governments have a policy of pretending that their citizens in these camps are not their responsibility. Several, including the UK, have started removing citizenship from those who have any discernible connection to another country, most recently and notoriously in the case of Shamima Begum. The views of those other countries on the matter are deemed to be irrelevant. I am not so daft as to say there are no security concerns to bringing these fighters back: Of course there are. This security challenge has been discussed by experts and policymakers since the start of the Syrian civil war. A famous study of foreign fighters prior to 2011 estimated that one in nine who returned to their country of origin would continue their extremist activities at home. As the author of that study told the British House of Commons Foreign Affairs Committee, this makes having traveled abroad to join an extremist terror group the single greatest predictor of participation in domestic terrorism. And, due to the unprecedented character of Daesh, we don’t know whether that figure still holds true — the Al-Hol case shows many remain committed to the group’s ideology despite its military defeat. But security concerns can be managed. There are also moral ones. Our attitude here might be described as extremist fly-tipping: We produced these fighters and allowed them to travel to Syria and Iraq to spread their misery. Now they have been defeated in battle, at great cost, we disclaim all responsibility for them. This is not acceptable. It is a useful exercise — in international as well as personal relations — to imagine our actions done in reverse: Syrian fighters coming in vast numbers to devastate large parts of the UK and, when we finally defeat them, Damascus refuses to take them back. The outcry would be unimaginable; there would be demands to force Syria to accept them, or else simply to reintroduce the death penalty. Europe’s hypocrisy is particularly revealing when one remembers the outcry over Guantanamo Bay. Peter Welby France has shown a double standard on the latter approach. This year, refusing to take back seven citizens and one resident who had joined Daesh, it asked for them to be tried in the Iraqi courts instead. They were promptly sentenced to death, prompting an outcry in the West that focused not on France’s failure to take responsibility for its own people, but on the shortcomings of the Iraqi judicial system. Europe’s hypocrisy is particularly revealing when one remembers the outcry in its press and politics over the US treatment and trials of detainees at Guantanamo Bay, and its refusal to bring them to the mainland for a trial in the civilian court system. The European Parliament in 2006 voted overwhelmingly to condemn Guantanamo Bay, to call for its detainees to be released or tried, and condemned suggestions that they could be released to countries where they could face death or torture. It is a different story when it comes to the actions of EU member states. So if the West is not to demand that the countries that suffered from Daesh’s depredations should have to deal with the foreign fighters now, what can it do? The first thing is to think about whether its law is sufficient. One of the reasons commonly given for refusing to take back foreign fighters is that most of them could not be convicted under current law. There is precedent, in the UK, for creating retrospective law in cases relating to war: The 1991 War Crimes Act, which targeted Nazi war criminals. It still requires specific crimes to be identified, which is one of the challenges with the foreign fighters, but it creates a principle that retrospective legal action might be permissible in relation to war. The key identifier for the majority of detainees is not their specific crimes (except in a few cases), but rather their participation in an endeavor that was overtly and violently hostile both to their home country and to the global order. In the UK, such participation could be covered by a new Treason Act, as recommended by the think tank Policy Exchange in 2018, although its retrospective nature would need to be limited to the Syrian conflict. Other countries could take a similar approach. The greatest challenge for Western states is that to bring home and imprison the thousands of their citizens and residents in Syria and Iraq would cost a vast sum; moreover, they should not be put in ordinary prisons due to the risks of wider radicalization. New prisons should be built and specialist prison officers, psychologists, parole boards and probation officers trained in order to assess which of those brought home are safe to be released back into the community. Investment needs to be put into the security services to continue to monitor the threat. This kind of investment is vast, and politically unpopular. But it meets the first requirements of any state: To provide its people with security and justice. In any case, if the West is to maintain any global standing, it must be done.