Police found "very violent" pictures of corpses on Bouhlel's computer, along with searches for the recent Orlando gay bar attack and the murder of a police officer and his wife near Paris but no evidence he had contact with IS, which has claimed him as one of its "soldiers", Prosecutor François Molins said on Monday.
Bouhlel had, however, expressed support for IS and during the last week started to grow his beard, telling an acquaintance that it was for religious reasons.
He told a friend that he had got into the habit of watching IS hostage-beheading videos.
As well as commandos trained in Iraq or Syria, recent attacks have been launched by individuals "obeying calls for murder by terrorist organisations who privilege France as a target", Molins said on Monday.
"This fanatical and mortifying ideology can push certain individuals to take action in France, without them needing to go to Syria or receiving any precise instruction. As we’ve seen already in several cases, radicalisation can happen all the more quickly when addressed to disturbed individuals or to those fascinated by extreme violence.”
Unrestrained sex life
Until recently Bouhlel, who came to France from the Tunisian town of Msaken in 2005, "was not a practising Muslim, ate pork, drank alcohol, took drugs and had an unrestrained sex life", Molins said.
Patrons of the Nice gym where he was a regular until two years ago described him as a vain "show-off".
One woman on whom he had designs described him as someone "who chased after everything that moved".
A 74-year-old man questioned by investigators is said by some to have been among his lovers.
Evidence of planning attack
His police record includes complaints for "threats, violence, theft and acts of criminal damage" and he received a six-month suspended sentence in March for attacking a driver with a nail-studded plank, leaving him with a six-centimetre-deep wound in his skull.
Investigators have also found that he staked out the site of his attack, taking selfies on Nice's Promenade des Anglais, where he was to kill 84 people and injure many more.
The first evidence of his plan emerged about eight months ago when he photographed a newspaper headline about a man deliberately ramming a car into a café terrace.
From 1 July he started searching online for information on the Nice Bastille Day fireworks display and subjects such as "horrible fatal accident".