"Mohamed Sifaou, an expert on Islamic radicalisation also said on BFMTV that the radicalisation can even happen on the same day as a suicide attack because ".Islamic ideologists are saying that dying as a martyr forgives all sins".
Neighbours have described Bouhlel as a violent loner who liked to drink, lift weights and go salsa dancing.
All seven people taken in for questioning said Bouhlel was violent and unstable. In a stunning turn of events, ISIS-which ordinarily puts gay and bisexual men to death-apparently did not vet its latest hero before reflexively claiming responsibility for his actions.
The nation has been left wondering whether the attack, in which a Tunisian man plowed a 19-ton refrigerated truck through crowds gathered for fireworks on Bastille Day, could have been avoided - or whether it must adjust to a harsh new reality.
The prosecutor spoke hours after thousands of people massed on the waterfront promenade where the attack took place for a moment of silence.
"We've been here for three days now, crying out, crying out, crying out, crying out". Five people believed to be linked to the man who killed 84 people in Nice are in police custody according to a statement by the Paris prosecutor's office.
In an affidavit seen by AFP, an officer who was among three stationed at the end of the famed Promenade des Anglais described Thursday's bloody confrontation with Lahouaiej-Bouhlel. She said she was pushing her 2-year-old son in a stroller with her 5-year-old daughter in tow when the screaming and hysteria began.
A 21-year-old French medical student who volunteered to help at the Pasteur hospital said he had been one of many who helped with the bodies.
She said Stratton can not speak and does not remember the attack, "which is better".
"He would become angry and he shouted.He would break anything he saw in front of him", he said, speaking to reporters in his Tunisian hometown of Msaken on Saturday.
The young man on the left is reportedly among those missing
He was spotted at the wheel of a hired lorry driving along the Promenade des Anglaises on the Tuesday and Wednesday before the Thursday massacre.
More than 200 people were also wounded in the carnage wrought by Mohamed Lahouaiej Bouhlel on the seafront of this southern Mediterranean city.
Concerning the questions on the planning and the organization of the Bastille Day firework display in Nice, Valls said, "the investigation will get to the bottom of this". Buildings stood silent across the country.
France's prime minister said in remarks published on Sunday that the attack, which was claimed by Islamic State, was Islamist in nature and that Bouhlel had radicalised "very quickly". The official wouldn't comment on the content of the text messages or confirm reports that they included a request for more weapons.
Bouhlel's rapid radicalization has puzzled investigators. Friends and family said he hadn't been an observant Muslim in the past. The uncle said he learned about the Algerian recruiter from extended family members who live in Nice.
Investigators hunting for possible accomplices to Bouhlel arrested two people Sunday.
The French government has come under pressure for failing to thwart the third major attack on French soil in the past 18 months.
After a special security meeting, Defense Minister Jean-Yves Le Drian said French forces in the U.S-led coalition struck IS targets again overnight and on Saturday. French war planes have been involved in the operation in Iraq and to a lesser degree in Syria.
Brigitte Erbibou, a psychologist who has long worked in Nice, said Bouhlel's reported lack of religious conviction may not have precluded a sudden embrace of extremism, noting that people who have resorted to violence in the past can apply that instinct in other situations.
On Monday, French officials still had not been able to establish a link between the attacker and any militant organisations.