French investigators are piecing together a picture of the gunman who shot a policeman dead on the Champs Elysees, as the country prepares to vote in its most closely watched presidential election in decades.

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.

Police sources said he had served time for previous armed assaults on law enforcement officers.

Authorities are now trying to work out if Cheurfi had any accomplices in Thursday night’s attack.

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

Cheurfi, 39, a French national who lived with his mother in the eastern Paris suburb of Chelles, had been convicted for previous gun attacks on law enforcement officers going back 16 years.

“He was not on the security watch list and had shown no signs of radicalisation despite his many years in prison,” said Francois Molins, a French prosecutor.

Police found a note defending Islamic State near his body and believe he had “opened fire on the officers in the knowledge he would be killed by them”, a source close to the investigation told Reuters.

In addition to the assault rifle used in the attack, a pump action shotgun and knives were in his car, the police sources said.

Three of his family members have been placed in detention, the French interior ministry said.

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Cheurfi served 10 years in prison after firing on two plainclothes officers in 2001 as they tried to arrest him in a stolen car.

While in detention, he shot and wounded a prison officer after seizing his gun.

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 was released for lack of evidence.

A French interior ministry spokesman initially confirmed that a second man was being sought, based on information from Belgian security services.

Confusion over Islamic State claim

A potential second suspect was identified as Youssouf El Osri in a document seen by Reuters.

Belgian security officials had warned French counterparts before the attack that El Osri was a “very dangerous individual en route to France” aboard the Thalys high-speed train.

The warning was circulated more widely among French security services in the hour following the Champs Elysees attack.

A man with that name has since turned himself in at a police station in Antwerp, Belgium.

Islamic State, which has hundreds of French-speaking fighters, claimed responsibility for the Champs Elysees shooting soon afterwards, in a statement identifying the attacker as “Abu Yousif al-Belgiki [the Belgian]”.

El Osri’s connection with either the downed assailant or the man named by Islamic State remains unclear.

“We don’t understand why Islamic State has identified the wrong person,” said a police source.

“What does seem clear is that Islamic State was planning something.”

— ABC/wires