More recently, French and other European security services have grown increasingly alarmed by thousands of young, alienated Muslim citizens who have enlisted for jihad in the conflicts in Syria and Iraq.

In each decade, a familiar pattern has emerged: a radicalized minority of European Muslims — whether they have gone abroad for jihad or not — have been angered and inspired by wars the West has waged in the Arab world, Africa and beyond, and have sought to bring the costs of those conflicts home.

After French authorities swept up members of the Buttes-Chaumont group in the 2005, during his time in prison Chérif Kouachi came under the sway of an influential French-Algerian jihadist who had plotted to bomb the United States Embassy in Paris in 2001.

There, he also recruited a holdup artist named Amedy Coulibaly, the man who killed four hostages at a kosher supermarket in Paris on Friday.

It is unclear if his older brother, Saïd Kouachi, who also took part in the attack on the Charlie Hebdo newspaper office, was a member of the Buttes-Chaumont group, but the authorities have confirmed that the older brother spent time in Yemen between 2009 and 2012, getting training from a branch of Al Qaeda.

Dominique Many, one of the defense lawyers involved with the Buttes-Chaumont group, said prison had only hardened Chérif Kouachi’s radicalism. “He was much more radical when he was judged in 2008 than he was in 2005, when he was arrested,” he said. “So perhaps in jail he became what he is today, the Kouachi that we knew these last days.”