Mohamed Lahouaiej Bouhlel barreled a 19-ton truck into the crowd on July 14, killing 84 people and injuring more than 200.
The investigation underway since the night of July 14 has progressed and not only confirmed the murderous premeditated nature of Mohamed Lahouaiej Bouhlel's act but also established that he benefited from support and complicity.
France declared three days of national mourning for the Bastille Day massacre, in which the lorry careered for hundreds of metres along the Promenade des Anglais seafront, slamming into families and friends after a firework display marking the anniversary of the 1789 revolutionary storming of the Bastille.
On April 4 this year, Tunisian Chokri C., aged 37, sent Bouhlel a Facebook message reading: "Load the truck with 2,000 tonnes of iron. release the brakes my friend and I will watch".
Five suspects will today go before anti-terrorism judges investigating the attack that left 84 dead and over 300 injured.
While the Islamic State group (IS) claimed the attack, describing him as a "soldier", investigators have not found direct proof of his allegiance to the jihadists.
Prosecutor Francois Molins said his office, which oversees terrorism investigations, has information from Bouhlel's phone which shows searches and photos indicating he had been studying an attack since 2015.
In a statement, Mr Cazeneuve accused the paper of conspiracy theories and said several "heroic" national police - who killed the attacker after an exchange of fire - were stationed further down the promenade.
The Albanian couple allegedly helped 31-year-old Lahouaiej Bouhlel acquire the gun he used to shoot at policemen during his fatal drive. The suspects are four men; two French-Tunisians, a Tunisian and an Albanian and one woman of dual French-Albanian nationality.
Police findings appear to contradict initial claims that the attacker was a "lone wolf" and was "radicalized" quickly.
Pictures of Oualid apparently taken in the truck used in the attack were also found on Bouhlel's phone.
Investigators are now examining whether the men had connections to Islamic State or other extremist groups, Molins said.
Paris prosecutor François Molins said authorities found "revealing" online searches and photos on the cellphone and laptop belonging to Nice killer Mohamed Lahouaiej Bouhlel dating back to previous year, including photos of the 2015 fireworks display.
It is the fourth time the security measures have been extended since Islamic State attacked Paris in November past year, killing 130 people.
The extension of extra search-and-arrest powers for police was approved by 489 votes to 26 against shortly before dawn in France's National Assembly, the lower house of parliament.