A handwritten note praising the so-called Islamic State (IS) militant group was found near the gunman suspected of fatally shooting a police officer Thursday in Paris, anti-terrorism prosecutor Francois Molins said.
Molins identified the attacker during a news conference Friday as Karim Cheurfi, a 39-year-old who had a long police record that included a previous attempted attack on police.
Police arrested Cheufri in February, but were forced to release him because they lacked evidence for a prosecution.
The Islamic State group, which claimed responsibility through its news agency, identified the shooter as "Abu Yussef the Belgian," calling him "one of Islamic State's fighters."
French media is reporting the attacker had been identified by police as a resident of Seine-et-Marne who was imprisoned for several years for shooting at police officers in the early 2000s.
Molins said police are still trying to determine if Cheufri had any accomplices in the attack.
"He was not on the security watch list and had shown no signs of radicalization despite his many years in prison," Molins said.
U.S. President Donald Trump predicted on Twitter Friday the attack would have an impact on France's presidential election on Sunday.
Le Pen calls for border checks
The attack prompted far-right presidential candidate Marine Le Pen to call Friday for a reinstatement of border checks and the expulsion of foreigners who are on the watch lists of intelligence agencies. Le Pen was the only major French candidate to support Trump, who pledged to crack down on immigration, during last year's U.S. presidential election.
Le Pen said in a radio interview Friday, "France, has again known the barbarism of a terrorist attack at the very heart of our capital."
Le Pen, who has spoken in increasingly inflammatory terms during her campaign, said the police targeted in the attack "have paid the price of the fight against radical Islamism, this monstrous, totalitarian ideology that has declared war on our nation, on reason and civilization."
Police, meanwhile, have detained and questioned three family members of the gunman who was shot and killed in the attack.
Hollande links attack to terrorism
The Champs-Elysees, Paris' most iconic boulevard, was returning to its normal activities Friday, after a gunman killed one policeman and wounded two others on the world-famous street.
French President Francois Hollande said he is convinced the "cowardly killing" was an act of terrorism. The French leader Friday called together the government's security council and his would-be successors in the presidential election campaign to discuss if, and how, the attack might impact voting intentions.
Hollande's defense and security council meeting was part of government efforts to protect Sunday's vote, taking place under heightened security.
"We shall be of the utmost vigilance, especially in relation to the election," he told the nation on television.
Centrist candidate Emmanuel Macron urged the country not to "give in to fear." Macron suspended two rallies after the shooting on the Champs Elysees.
U.S. Vice President Mike Pence, speaking Friday in Jakarta, said the attack in Paris was the latest reminder that terrorism can strike anywhere and at any time. He said the U.S. would not relent in its efforts to end terrorism.
In Washington, President Donald Trump sent condolences to the French people. He called the attack "a terrible thing," and said it was another example of the sort of violence that "never ends."
France is on edge ahead of Sunday's presidential election, with a very close outcome expected. The country is still feeling the effects of a series of deadly Islamic terrorist attacks over the past two years that killed more than 200 people.