His father, Michel, was a respected butcher whose shop window looked out on the cobblestoned town square. His sons worked in the shop as teenagers, and Jerome pursued the trade for a time. He was raised Roman Catholic. When his fathers business failed, he began drinking alcohol and doing drugs. By 1997 he had converted to Islam, and moved to London, where he came under the influence of radical Muslims. They frequently attended the same mosque as Zacarias Moussaoui, and allegedly befriended him.
Upon returning to France, he was placed on the CIA terrorist Watchlist. The French police were alerted of this after he was arrested for shoplifting a pair of shoes in Calvados, France. Jerôme Courtailler spent six months in jail.