Authorities have now detained seven people over the killings, claimed by Islamic State.
The 31 year-old Tunisian killer, Mohamed Lahouaiej Bouhlel, drove at the crowd in the Riviera city on Thursday night, zig-zagging along the seafront Promenade des Anglais for two kilometres as a fireworks display marking the French national day ended, until police eventually shot him dead.
French authorities have yet to produce evidence that he had turned to radical Islam. Nevertheless, Interior Minister Bernard Cazeneuve said Bouhlel may have undergone a rapid change.
Attacker visited site with truck twice
Tunisian attacker Mohamed Lahouaiej-Bouhlel visited the Nice promenade with his rented truck on the two days before he rammed the vehicle into a crowd, killing 84, a source close to the investigation said Sunday.
The source said police had questioned hundreds of people since Thursday night's attack, several of whom said Lahouaiej-Bouhlel did show signs of being religious.
French authorities have said the attacker became radicalised "very quickly", and some of his family and friends had previously said he smoked, drank and never went to the mosque.
