Many of France's most committed Islamic radicals learned their murderous ideology in jail, and it is among these vulnerable prisoners that the French authorities are trying to fight back.
A groundbreaking program of deradicalization involves separating out volunteer prisoners into dedicated units, putting them face to face with the victims of Islamic terror, and bringing them together with secular sociologists, non-Muslims and other members of the community whom they have been taught to abhor.
The program is in its infancy, and already it has been criticized, in particular for gathering radicals so they can 'talk shop.' It is, however, a key plank of the wider strategy on confronting jihadism.
Journalist Christophe de Bellaigue explores these issues through interviews at the Osny prison, where the program is being piloted.