One of the most enduring images summing up the insidious and far-reaching spread of ISIS’s poisonous ideology was that of three schoolgirls from east London in 2015, looking for all the world as if they were heading off on a school trip rather than their more terrifying mission of leaving British shores for the extremist group’s so-called caliphate in Syria.
One of those 15-year-olds, Shamima Begum, now wishes to return to the UK and the authorities’ indecision about how to deal with her, pregnant but remorseless, sums up a global dilemma: what should be the fate of foreign fighters who joined ISIS but wish to return home?
Ms Begum's family has pleaded for compassion and forgiveness; she has said she wants a quiet life but has no regrets. She is one of an estimated 41,490 foreign recruits to the terrorist group from 80 countries, of whom at least 1,000 are being held in Syria by the US-backed Syrian Democratic Forces. There are fears if the US withdraws its presence in Syria, they could escape.
Complicating the matter still further is the question of what to do with those who have returned, or want to – whether a jail term is sufficient or whether an extensive deradicalisation programme is needed to ensure they do not become killers again.
There is also the danger of them radicalising others if they spend time in prison. After a series of attacks leaving hundreds dead, France has experimented with isolating extremists in prisons and reintegration programmes, with mixed degrees of success.
British authorities have veered between suggesting they should never be allowed to return, to hunting and killing them, or, in the words of former MI6 director Richard Barrett, treating the likes of Ms Begum as going "badly off the rails".
MI6 chief Alex Younger, however, told the Munich Security Conference returnees were unlikely to reconcile with their homelands and posed a new security threat.
Empathy and compassion will undoubtedly be in short supply for those who thought nothing of terrorising, maiming and killing innocent citizens. But equally, governments that absolve themselves of the responsibility of investigating their crimes and meting out appropriate punishment run the risk of those extremists disappearing, only to reform and re-emerge elsewhere to rain down terror once again.
A global conversation must be had about the fate of returning fighters before they pose an even greater threat. It is urgent and essential to prevent the ugly head of ISIS, or its next incarnation, from rising again.