Members of French special police forces of Research and Intervention Brigade (BRI) leave following a police operation the day after a shooting in Strasbourg, France, December 12, 2018.   REUTERS/Vincent Kessler
Death toll rises to 5 in Strasbourg terror attack
01:08 - Source: CNN
Paris CNN  — 

The man responsible for a fatal Christmas market attack in the eastern French city of Strasbourg pledged allegiance to ISIS, a judicial source with knowledge of the investigation told CNN.

“A video in which Chérif Chekatt pledged allegiance to ISIS was found on a USB key,” the source said. It was found during the police search, the source said, but declined to provide further information.

The December 11 attack left five people dead and about a dozen people injured. Chekatt was killed during a shoot-out with police in Strasbourg two days later.

Cherif Chekatt was killed in a shoot-out with police.

Following the gun and knife attack, ISIS claimed through its Amaq news agency that the assailant was a “soldier” of ISIS. However, the terror organization offered no evidence of advanced knowledge or planning involved in the attack.

Chekatt, 29, was known to prison officials for being radicalized and for his proselytizing behavior in detention in 2015, Paris prosecutor Rémy Heitz said earlier this week, adding that he had been incarcerated multiple times in the past.

French prosecutors said the suspect shouted the Arabic phrase “Allahu Akbar,” meaning “God is greatest,” at the time of the attack.

Chekatt also had an extensive criminal background in Germany and Switzerland for thefts, break-ins and violence but neither country had him on a radical Islamist list.

CNN’s Saskya Vandoorne contributed to this report.