The Bastille Day attacker who killed at least 84 people in the French Riviera city of Nice had been planning the attack for months with the help of at least five accomplices, the Paris prosecutor has said.
"The investigation under way 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," Francois Molins told a news conference.
The prosecutor said he had placed the five people – an Albanian couple, a Tunisian man and two Franco-Tunisian men - under formal investigation after they were taken into custody.
None of them had been known to intelligence services.
The 14 July attack by the Tunisian delivery man at peak holiday time on the Riviera plunged France into new grief and fear, just eight months after 130 people were killed in a series of coordinated attacks in Paris.
More than 400 investigators have been poring over evidence since the attack in which Bouhlel drove a truck into crowds celebrating France's national holiday. More than 300 people were also injured.
Records of Bouhlel's phone use indicated a large number of exchanges, calls and text messages over the last year with several of the accomplices under investigation, he said.
Bouhlel received a text from one of the men a few days after the January 2015 Islamist attacks on the Charlie Hebdo newspaper and a Jewish deli saying: "I am not Charlie ... I am glad, they brought in Allah's soldiers to finish the job."
A day after that text was sent, on 11 January, millions of French people rallied in Paris and other French cities under the slogan "Je Suis Charlie" (I am Charlie) in solidarity with the victims at the satirical newspaper.
The so-called Islamic State has claimed the Nice attack, calling Bouhlel one of its soldiers, but authorities say they have yet to find evidence that the 31-year-old, who was shot dead by police, had any actual links to the militant group.
One of the suspects filmed the scene of the attack, on Nice's Promenade des Anglais, the day after the attack as the area was full of police and journalists.
Mr Molins said prosecutors had requested five suspects be charged with conspiracy to commit terrorism, among other crimes.
