The gunman who killed a French police officer on the Champs-Elysees on Thursday was convicted in 2003 of attempted homicide in shootings on two police officers, two French officials said on Friday.
Karim Cheurfi, 39, had spent 13 years in prison for non-terrorist offences including the attempted murder in 2001 of police officers, anti-terror prosecutor Francois Molins said.
He had not shown any signs of radicalization while in prison or while under judicial supervision after his release, Molins said.
Molins said Cheurfi had been arrested in February after authorities became aware that he had tried to acquire weapons and had spoken in terms that suggested he wanted to kill police officers.
Searches and a phone tap carried out at the time found no evidence that he had adopted radical Islamic ideas or was viewing extremist websites.
Investigators found that he had bought hunting knives, masks and a go-pro camera online but there was not sufficient evidence to bring charges.
Belgium's Interior Minister Jan Jambon later said that the shooter was a French national.
Meanwhile, French police took into custody three family members of the gunman who was killed at the scene, a legal source said.
A French policeman was shot dead and two others were wounded on the Champs-Elysees in central Paris on Thursday night in an attack carried out days before presidential elections and quickly claimed by the Islamic State militant group.
According to an AFP report, a note backing the Islamic State group was found near the shooter, a source familiar with the investigation said.
President Francois Hollande said he was convinced the "cowardly killing," in which the assailant was himself shot dead by police, was an act of terrorism.
Meanwhile, a man that Belgian authorities had flagged to their French counterparts over possible involvement in Thursday's shooting turned himself into police in Belgium's northern city of Antwerp, and was found to have no connection to the attack, authorities said.
A prosecutor in Belgium's Antwerp said, "That man came to police late yesterday after he saw himself appear on social media as terror suspect No. 1 relating to yesterday's facts."
The prosecutor, who declined to be identified because the investigation was ongoing, said the man had nothing to do with the attack. "He was not part of a terrorism investigation."
France has fully mobilized its security forces, including elite units, to ensure citizens' protection during the forthcoming presidential election following the shooting, Prime Minister Bernard Cazeneuve said on Friday.
Speaking after an emergency meeting of top security officials, Cazeneuve said all elite units were on top alert for the election to back up the 50,000 police already earmarked for special election duty.
"The goverrnment is fully mobilized. Nothing must be allowed to impede the fundamental democratic process of our country. It falls to us not to give in to fear and intimidation and manipulation which would play into the hands of the enemy," he said in a statement.
The first round in France's two-stage election will be held on Sunday with a second final round on May 7.
Belgian federal prosecutors said Friday there was no indication that the perpetrator of the attack held Belgian nationality himself, this despite the fact that ISIS said the his name Abu Yousif al-Belgiki.
"Al-Belgiki means the Belgian but it is a very vague identity," a spokesman for Belgium's federal prosecutor said, adding he had no indication the gunman was from Belgium.
Belgian Interior Minister Jambon said the name given by ISIS was altogether wrong, saying he "is certainly not the guy who committed the crime yesterday."
In November, 2015, when Paris was rocked by near simultaneous gun-and-bomb attacks on entertainment sites, two of the 10 known perpetrators were Belgian citizens.
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