The alleged gunman who shot and killed five people in a Christmas market attack this month in Strasbourg had pledged allegiance to the Islamic State group, according to an official.

The French judicial official said investigators have found a video stored on a USB stick in which Cherif Chekatt had claimed allegiance to the extremist group.

The video was discovered at Chekatt’s home.

Chekatt, 29, died in a shootout with police two days after his December 11 attack at Strasbourg’s popular Christmas market.

Shortly after his death, the Islamic State group’s Amaq news agency claimed he was a “soldier” of the group.

French Interior Minister Christophe Castaner had rejected the claim as “totally opportunistic”.