A week after Bouhlel rammed a truck into a crowd which had been enjoying a Bastille Day fireworks display, killing 84 people, Molins said photos on his phone showed he had likely already staked out the event in 2015.
It also emerged that one of the five suspects in custody, a Tunisian named Mohamed Oualid G., had filmed the scene of the crime the day after the carnage, as it crawled with paramedics and journalists.
The five suspects will be presented to anti-terrorism judges later Thursday and Molins said prosecutors had requested they be charged with conspiracy to commit terrorism, among other crimes.
They are 22-year-old Franco-Tunisian Ramzi A., 37-year-old Tunisian Chokri C., 40-year-old Tunisian Mohamed Oualid G., 38-year-old Albanian Artan H., and his wife Enkeledja Z. who holds both French and Albanian nationality.
None of the suspects was known to intelligence services, and only Ramzi A., who was born in Nice, had a criminal record for robbery and drug offences.
This suspect led police to discover a Kalashnikov and a bag of ammunition on Thursday, however their purpose was unclear.
More than 400 investigators have been poring over evidence since the grisly attack, the third in France in 18 months, and it was analyses of Bouhlel's telephone that led them to the five suspects.
Bouhlel was shot dead by police after his rampage.
While the Islamic State group claimed the attack, describing him as a "soldier", investigators have not found direct proof of his allegiance to the jihadists.
Many people interviewed by investigators described the Tunisian father of three as "someone who did not practise the Muslim religion, ate pork, drank alcohol, took drugs and had an unbridled sexual activity", Molins said earlier this week.
However initial details of the investigation reveal his fascination with jihad has been around for a while.
On May 26 last year, he took a photo of an article about the drug Captagon, an amphetamine used by jihadists in Syria.
