Peter Neumann discusses the European returnees dilemma on CNN Amanpour

After every conflict we have the same problem. In fact, after the Soviet invasion of Afghanistan ended and the fall of the communist regime in Kabul, many of the veteran volunteers of the Afghan jihad returned back home and they started a campaign of terrorism in many countries, including Algeria and Egypt. And as a result, basically this is not a new phenomenon, but at the time there weren't many Europeans. Now we have Europeans.

Yeah, I mean, in Europe for the last several years, it's been the most significant mobilization of jihadist foreign fighters that has ever happened. It's estimated that between five and six thousand Europeans have gone to Syria and Iraq. And of course, going back to your question, they've not only been returning since recently, they've been returning for years. So for example, British government estimates that already 400 are back in the country. So when President Trump tweeted this weekend, it wasn't him causing this situation; he was prompting or addressing something that's been happening for a number of years and that's become more urgent now because everyone is that this Kurdish Syrian autonomous region is going to collapse and that a lot of people that are currently in the captivity of the SDF, of the Kurds in Syria, are going to be free. Yet so those of course are the US allies who are fighting ISIS on the ground, and as you say, what's to become of these people if that whole area falls apart?

I think right now it's not very good. However, I want to emphasize that we need to see this in context. So from our experience having watched a lot of these fighters going to Syria, the experience of Syria causes typically one of two reactions. Some people have become more radicalized, have become brutalized and are utter wrecks. It's very difficult to de-radicalize them; it's not possible to de-radicalize everyone. Other people, however, have been turned off by the experience with ISIS, perhaps similar to you, and are ready to leave and to leave that experience behind and perhaps are able to open up. So for those people who have radicalized further, absolutely they should be prosecuted and they should be locked up as long as they pose a threat to society. But those who have turned away, they should be given the opportunity to open up and perhaps even for that evidence that they use to be used against other people who are more difficult cases. That would, in my mind, be a smart strategy of dealing with people who are British citizens and who because of that actually have a right to come back if they choose to do that.

I mean, it's Trump just saying what may happen anyway. If this place where the Kurdish, the Syrian Kurds collapses, the YPG, the SDF, and they can't hold them anymore, is he just talking about what's obviously going to happen? Personally, I think well, it's happening because Trump is withdrawing from Syria, and everyone assumes, all the experts assumed, that without the American support, the Kurdish autonomous region will not be strong enough to survive. And so I personally think we have a window of about 12 months to bring these people back. So my 18... 12 months? Well, because Trump said March, April he wants the last American troops to be out. I think the Kurds can survive for about eight months against the Turks, but of course their priority will be to fight against the Turks, not necessarily to keep ISIS fighters from countries who they don't even care about. And who's afraid of them, by the way? Absolutely. And so within 12 months, I do think most European countries will have to successively bring some of these people back, unless they want them to be uncontrolled across the region, perhaps even smuggling themselves back into European countries. So my recommendation would be: bring them back, bring them back successively. Start with the easy cases, use the evidence that they provide you with in court against the more difficult cases. So sort of a chain situation.

In France, two weeks ago the government said we're going to bring all of our citizens back, 130 of them, all at once. I think that's a mistake because the French currently do not have the capacity to deal with so many people, including women and children, and prosecute them. I do think the best way is to bring them back successively, one by one almost.

How well? All I can tell you is that you have to use the stick and the carrot. You have to weaponize kindness on one hand and you have to have a strong deterrence on the other. For the easy cases, for those who cooperate, you use leniency and heavy monitoring. For those who don't cooperate, it's a very radical problem that requires a radical out-of-the-box solution, which means you build an offshore facility on an island that is yours legally, and you put them there far away from the general population. Because nothing that the jihadists fear more than anything is isolation far away from the general population. So that is how you deal with it. On one hand, those who cooperate, admit them back to society in stages. Those who do not, the hardcore cases, you put them on an island somewhere. It is that sort of Guantanamo-like facility, but legally your jurisdiction. So basically the UK will have lots of islands around the world governed by UK rules and regulations, but you build the facility there because this is a different kind of threat. The problem is they are not your usual criminals where if you put them into prison, they know the errors of their way and they are punished. These people, if Shamima for example comes back and she is put into prison, what she will do? She will create 20 other Shamimas. Well, that's where you can say because prison is a radicalizing environment. That's the point I want to make.

But you're absolutely right to raise the point about prisons. Because one thing is to prepare to get people prosecuted and convicted. The second step is to think about prisons: do we have the capacity? How do we prevent people from radicalizing other people within prisons? And then the third step is to think about prevention and rehabilitation for those cases where we think that is appropriate. And one thing we haven't thought about enough is most of these rehabilitation programs are for young men, and we now expect a lot of women to come back. We do expect kids, very young people, to come back who are both victims and potential perpetrators both at the same time. And that requires a lot of psychological...

Hmm. So I think there are three... I mean, not in her case because it's very obvious, but three sources of evidence. One is secret intelligence information. The second point is especially people who went early in 2014 were still posting a lot of stuff online. There's a lot of social media that has been confiscated that can be used. The third source, like in every criminal case, is other people who were with them. And we know that especially with European foreign fighters who often didn't speak Arabic, they were staying with other people who spoke the same language. So you can assume that Shamima knows a lot of other English fighters and they know her. And once you get four or five of them to open up and implicate others, you can use that as evidence in court. So I refer to the Beatles, they're the four major known killers, captors of the journalists and the aid workers in ISIS.