Police check passers-by near the Champs Elysees in Paris after a shooting which left one officer dead and two wounded.
Cheurfi was detained two months ago after speaking threateningly about the police but released for lack of evidence, according to two police officials, speaking to AP on condition of anonymity.
They also reported he was convicted of attempted homicide in 2003 in shootings on two police officers.
The Champs-Elysees gunman who shot and killed a police officer just days before France's presidential election was detained in February for threatening police but then freed, two officials told The Associated Press on Friday.
CBS News spoke with a tourist who witnessed the shooting and said a man started shooting at police and seconds later police returned fire and he went down.
France has been in a state of emergency since a spate of terror attacks hit the country in 2015.
The Paris prosecutor's office said counterterrorism investigators are involved in the probe.More news: Iran not living up to 'spirit' of nuclear deal, says Donald Trump
President Francois Hollande said that he was convinced the attack was "terrorist-related".
Several candidates in Sunday's presidential election have ended their campaigns early as a mark of respect, with the centre-right's François Fillon calling on others to halt theirs too.
ISIS claimed responsibility for the attack, but at this point, it is unclear if the attacker, 39-year-old Frenchman Karim Cheurfi, acted alone or not.
The terrorist network's news agency identified the attacker as Belgian man Abu Yusuf al-Baljiki in a tweet taking credit for the Thursday night attack, the New York Post reported. Cazeneuve, the Socialist prime minister, accused the National Front leader of seeking to make political hay from the assault. The shooter got out of his auto and started firing at police, Brandet said on BFMTV.
It was the sixth terror attack in Paris in the last 3 years.
Speaking in Indonesia Friday, US Vice President Mike Pence said the attack was just the latest reminder "that terrorism can strike anywhere at anytime".
Said by polls to be running neck-and-neck with Le Pen, he tore into her claims that previous attacks wouldn't have happened under her watch. Officials later said a tourist was injured by fragments from the shooting.More news: Paris police officer killed and two injured in suspected terrorist shooting
"She won't be able to protect our citizens", Macron said.
Paris police spokeswoman Johanna Primevert told AP the gunman deliberately targeted police on guard near the Franklin Roosevelt subway station.
In November, 2015, Paris was rocked by near simultaneous gun-and-bomb attacks on entertainment sites, in which 130 people died and 368 were wounded.
Pictures of the scene in Paris showed people rushing to clear the area, and a heavy armed police presence.
The gunman pulled up in auto alongside a parked law enforcement van and opened fire with an automatic weapon, CBS2's Brian Conybeare reported. France's interior ministry said the attacker was killed in the incident in the early evening on the world-famous boulevard.
The attack appeared to fit in a spreading pattern of French extremists targeting security forces and symbols of the state, to discredit, take vengeance and destabilize.
In February, a man armed with a machete in each hand attacked soldiers on patrol at Paris's Louvre Museum.More news: USS Carl Vinson was sent to Indian Ocean, not Korean Peninsula
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