Questions arose Tuesday over how a known radical Islamist who rammed a car laden with weapons and gas canisters into a police van on Paris's Champs-Elysees was able to hold a firearms licence.
Adam Djaziri, a 31-year-old who had been on a watchlist for radical Islamists since 2015, was killed on Monday as his car smashed into the police van on the French capital's most famous avenue.
Two handguns and a Kalashnikov-style assault rifle were found in the car, while a weapons stash was discovered at the home of the attacker.
A source close to the inquiry said a letter had been found in which Djaziri claimed allegiance to Islamic State group leader Abu Bakr al-Baghdadi.
Djaziri's father, who has since been detained, told AFP his son practised shooting as a sport, and a source close to the probe said he had nine registered weapons including pistols and an assault rifle.
In the letter, Djaziri boasted that he was playing a "double game" by amassing weapons for an attack by posing as a shooting enthusiast, the source said.
The head of the French Shooting Federation said police officers had visited Djaziri's shooting club to enquire about him -- implying that his keen interest in guns had raised suspicions.
The attempted attack comes as France remains under a state of emergency after a wave of jihadist assaults that have left more than 230 people dead since 2015.
As the month-old government of President Emmanuel Macron prepares to unveil a tougher new anti-terrorism law, Prime Minister Edouard Philippe expressed dismay that Djaziri was able to have a gun permit.
"What I know at this stage is that the first weapons permit was given before this individual was flagged up," he said in an interview with BFM television and RMC radio, but he added that "no one can be satisfied -- and certainly not me" that Djaziri was able to possess dangerous weapons after being put on a watchlist.
French Shooting Federation chief Philippe Crochard said Djaziri had been licensed for six years, and a source close to the probe said the attacker had requested a renewal of his permit in February.
"Two policemen came in October 2016 and asked questions about this person. It isn't normal procedure, so I assume they had their reasons," Crochard told AFP.
Djaziri's ex-wife, brother and sister-in-law were detained late on Monday after police questioned them at the family home in Plessis-Pate, south of Paris. Djaziri's father was also taken into custody, a judicial source said.
Raised in a strictly Salafist Muslim family, Djaziri had no criminal record but caught the attention of authorities after making several trips to Turkey -- a route used by many European fighters heading to Syria -- which he said were for work.
Burn marks were found on Djaziri's body but it was not yet clear how he died. There were no other casualties from the attempted attack.
Since the large-scale Paris attacks in November 2015 and last year's Nice truck attack, France has suffered a string of smaller assaults targeting security forces.
Djaziri died just a short distance from the spot on the Champs-Elysees where a jihadist shot dead a police officer two months ago.
Earlier this month an Algerian man attacked a policeman with a hammer outside Notre Dame cathedral, another key tourist draw, while troops shot dead a man at the capital's Orly airport in March after he attacked a soldier on patrol.
In February, a man armed with two machetes assaulted four soldiers patrolling outside the Louvre museum.
Interior Minister Gerard Collomb said Monday that the Champs-Elysees incident "shows once again that the threat level remains extremely high in France".
Few details have emerged of the new anti-terrorism law due to be unveiled Wednesday.
But a draft leaked to the daily Le Monde has sparked concern among civil liberties campaigners who worry it could make some emergency measures permanent, such as the ability to conduct searches at any time of day or night and to restrict suspects to a certain geographic area.
The bill may also empower officials to shut down places of worship on the grounds of seeking to prevent a possible future attack.
The current state of emergency is due to expire on July 15 but the government is seeking to extend it until November 1.