The Paris prosecutor says the Champs-Elysees attacker had a note defending the Islamic State of Iraq and Syria (ISIS) with him when he opened fire on police officers.

Anti-terrorism prosecutor Francois Molins said during a news conference Friday that the note apparently fell out of the pocket of Karim Cheurfi, a 39-year-old with a criminal record.

Molins says the note praised ISIS and listed the addresses of security sites.

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The extremist group claimed Thursday’s attack in which one police officer was killed. Cheurfi was shot and killed by officers.

Molins said Cheurfi had a long police record, notably for trying to attack police in the past. The prosecutor said Cheurfi was arrested in February, but later released for lack of evidence of a threat.

Cheurfi’s former lawyer says his client most likely had “psychological” problems that he didn’t get proper help for.

Speaking Friday on BFM-TV, lawyer Jean-Laurent Panier described Cheurfi as an “extremely isolated” individual, one who passed near unnoticed while in detention. Panier said Cheurfi never spoke about religion, adding “his only conversations were about how to fill his daily life with video games.”

U.S. authorities told CBS News that Cheurfi has not shown up in any U.S. databases of terrorists and overnight data scrubs had not revealed any links between Cheurfi and people in the U.S.

As customary, U.S. law enforcement and intelligence agencies are in touch with French authorities and will assist as needed.

The policeman killed on Paris’ most famous boulevard has been identified as Xavier Jugele by Flag!, a French association of LGBT police officers.

The group’s president, Mickael Bucheron, told the Associated Press the slain officer would have celebrated his 38th birthday at the beginning of May.

Jugele was among the officers who responded to the gun and bomb attack on Paris’ Bataclan concert hall in November 2015, part of a wave of assaults in the French capital that killed 130 people, he told People.com when the venue reopened a year later with a concert by Sting.

People quoted him as saying how happy he was to be at the “symbolic” reopening, “here to defend our civic values.”

“This concert’s to celebrate life. To say ‘No’ to terrorists,” it quoted Jugele as saying.