At least one Frenchman was among the Islamic State militants shown in a video beheading captured Syrian soldiers, the chief prosecutor of Paris said.

Maxime Hauchard, a 22-year-old convert who left for Syria in August 2013, has been identified as one of the killers, Francois Molins, the prosecutor, said at a press conference in Paris today. Investigators believe there may be another French convert of the same age among the militants in the video, and are working to identify him, Molins said.

In the video, which also appears to show the severed head of U.S. aid worker Peter Kassig, at least a dozen men identified as Syrian soldiers being led one-by-one by Islamic State fighters, forced to kneel, and then beheaded.

The presence of Hauchard in the footage was first announced by French Interior Minister Bernard Cazeneuve earlier today.

Hauchard, who is from Normandy in northwestern France, converted to Islam at 17 and had been followed by French police because of his increased radicalism, though hadn't committed any acts that would have warranted his arrest before he left for Syria, Molins said. He first studied at Koranic schools in Mauritania before leaving because he didn't find them extreme enough, according to the prosecutor.

Molins said 1,132 French residents are currently in Syria and Iraq with radical Islamic groups, of which 90 are women. Cazeneuve said this morning that 138 veterans of the Syrian conflict have been arrested upon their return to France, and that 90 have been charged and 68 jailed.