PARIS — Ten young Muslim men, bored by a mundane life in France and haunted by a “feeling of uselessness,’’ as one put it, were seduced by a leading Islamic State recruiter in Europe in 2013. Within months, they were in Syria under the watchful eyes of hooded, Kalashnikov-wielding militants, doing push-ups, fiddling with weapons, and imbibing the ideology.
But the harsh regimen, most have since told investigators, was not to their liking, and it was not long before they hastened back to their families in the Strasbourg area, where they were almost immediately picked up by French authorities.
What to do with hundreds, perhaps thousands, of such young men in Europe is now among the biggest challenges facing governments and security services.
After the Paris and Brussels terrorist attacks, which were carried out in part by Europeans who had spent time in Syria with the Islamic State, France and other countries are grappling with how far to go in tightening laws to prosecute, monitor, and restrict the movements of returnees.
At the heart of the debate is whether to take preemptive legal action against people who have not committed terrorist acts or even been implicated in a plot but who have simply been to Syria and possibly received training in Islamic State camps.
Several urgent factors have propelled the debate: the steeper risks of terrorist attacks, the fact that monitoring the sheer numbers who have returned is overwhelming security services, and the difficulty of building cases against suspects who may have been trained and indoctrinated in distant lands.
At least 14 European countries have made receiving terrorism training a criminal offense. Nine have made travel from the war zones of Syria and Iraq an offense.
In France, more than 900 people have left the country to be jihadis, making it Europe’s biggest wellspring of foreign fighters. The government is now debating whether to allow house arrest even if there are merely “serious reasons for thinking’’ someone has been in an overseas war zone.
Two trials involving French jihadi cells were held in Paris this month, with the defendants in one of them receiving sentences of up to 10 years on charges of “criminal conspiracy with the aim of preparing acts of terrorism.’’
Setting policy for dealing with returning jihadis is just one example of how Europe, like the United States after the Sept. 11 attacks, is being forced to weigh security concerns against civil liberties.
Even before the Paris and Brussels assaults, cases like the one in Strasbourg were highlighting the difficult choices posed by European citizens coming home from Syria.
At least 1,300 European jihadis have returned to the Continent, and those are only the ones identified by the police. Three times as many Europeans may have gone to Syria, some slipping back undetected, with disastrous con-sequences.
One member of the Strasbourg group, Foued Mohamed-Aggad, returned after the others and was not detected by the authorities. He ended up as one of the three killers at the Bataclan concert hall in Paris, where 90 people were shot dead Nov. 13.
Of the nine others from Strasbourg known to have gone to Syria, two were killed there in January 2014, but seven returned and were quickly arrested in May 2014. They are awaiting trial.
The record of their interrogations afterward is a dance of denial that they intended any harm in Europe.
“This is a radical, extremist Islam, which has nothing to do with basic Islam and which I disavow,’’ Mohamed-Aggad’s brother, Karim, told investigators, according to documents recounting the interrogations.
