French investigators are trying to determine the true identity of the man wearing a fake explosives vest who tried to attack a Paris police station with a butcher knife, inspecting the dead assailant's phone and a note he was carrying.

Paris prosecutor Francois Molins said the assailant shot dead on the anniversary of the Charlie Hebdo attacks gave his nationality as Tunisian and carried a paper marked with the Muslim declaration of faith, an emblem of the Islamic State group, and a name. He also had a phone with a German SIM card, Molins said.

"I am not at all certain that the identity he gave is real. This identity has been checked with the intelligence services and he is not known under this name by the intelligence services," Molins told France-Inter radio Friday.

Instead, police are "working on the hypothesis" that the assailant is a man who was involved in a minor 2013 robbery in the southern Var region, according to a French security official who spoke on condition of anonymity because he was not authorized to discuss the case.

The official said that the fingerprints of the dead attacker matched those of the robbery suspect, who identified himself at the time as Ali Sallah of Casablanca, Morocco. But the assailant Thursday appeared to be older than 20, which would be his age under the ID he verbally gave police in 2013. He provided no papers and described himself as a homeless Moroccan in France illegally, the official said.

Authorities say the assailant was shot to death after he ran up to the police station in northern Paris with a butcher knife and refused orders to back away. Molins said a piece of paper found on him offered allegiance to the leader of the Islamic State group and said "his act is linked to the deaths in Syria." The shooting came exactly a year after two Islamic extremists attacked Charlie Hebdo, killing 12 people at the satirical newspaper's office.

The Islamic State group has claimed responsibility for the January 2015 attacks that killed 17 and the Nov. 13 attacks in Paris that killed 130.

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Associated Press writer Philippe Sotto contributed.