Police seek possible accomplices of Paris gunman

• Paris gunman's criminal past in focus as police hunt second suspect
• Gunman targeting white men kills three in Fresno, California
• Gunman kills 39 in Istanbul nightclub attack, manhunt under way

The gunman, identified as Karim Cheurfi, opened fire on a police vehicle parked on the Champs Elysees in Paris late on Thursday, killing one officer and injuring two others before being shot dead.

The attack, which was claimed by Islamic State, overshadowed the last day of campaigning for Sunday's presidential election first round.

A damaged window is pictured on the Champs Elysees Avenue the day after a policeman was killed and two others were wounded in a shooting incident in Paris, France, April 21, 2017. REUTERS/Benoit Tessier

Cheurfi, 39, a French national who lived with his mother in the eastern Paris suburb of Chelles, had spent some 14 years in prison from 2001 for crimes including gun attacks on law enforcement officers.

"The investigations will now focus on determining ... the potential help that he may have benefited from," Paris Prosecutor Francois Molins told a news conference on Friday.

"He was not on the security watch list and had shown no signs of radicalisation despite his many years in prison."

But Molins confirmed police had found a note with handwritten messages defending Islamic State near his body, addresses of police establishments in his car and a Koran.

French police arrive at the house of the gunman killed in a shootout with police on the Champs Elysees Avenue, in the Paris suburb of Chelles, France, April 21, 2017. REUTERS/Charles Platiau

Police believe he had "opened fire on the officers in the knowledge he would be killed by them", a source close to the investigation said.

As well as the assault rifle used in the attack, a pump action shotgun and knives were in his car, Molins said. Three of his family have been placed in detention, the French interior ministry said.

Cheurfi served 10 years in prison after firing on two plainclothes officers in 2001 as they tried to apprehend him in a stolen car. While in detention, he shot and wounded a prison officer after seizing his gun.

Police secure the Champs Elysees Avenue after a shooting incident in Paris, France, April 20, 2017. REUTERS/Christian Hartmann

Released on probation in 2015 from a further two-year jail term imposed for lesser offences, Cheurfi was arrested again in February after threatening to kill police officers - but released for lack of evidence.

Before that arrest he had travelled to Algeria for about a month despite probation conditions forbidding him to leave the country, Molins said, adding that the judge had opted not to send Cheurfi back to prison.