At least 10 children were among the dead, French prosecutor François Molins said Friday. "They had to stay there for a couple of hours, but people wouldn't even come out - they were so frightened - until the police came and said it was OK to come out", he said.
Lahouaiej-Bouhlel, born on January 31, 1985 in the Sousse suburb of Msaken, was married to a Franco-Tunisian resident of Nice. He had a permit to live and work in France.
Online news reports have emerged claiming Bouhlel, who worked as a delivery driver according to Nice Matin, had told police he was dropping off supplies of ice cream.
The man was "entirely unknown by the intelligence services, whether nationally or locally", Molins said.
Neighbors in his apartment building told CNN's Nic Robertson they often saw him walking or riding his bicycle to a cafe for a cup of coffee.
"France is afflicted, but she is strong, and she will always be stronger than the fanatics who want to strike her today", he said.
The middle-aged woman was visibly upset while speaking to CNN.
"We would hold the door open for him and he would just blank him", Jasmine said.
Police found the terrorist had rented the truck a few days ago from a specialist garage at Saint Laurent du Var by Nice Airport and boarded the lorry in the hills around Nice.
He later said Bouhlel had been picked up on CCTV cameras getting into the truck "in the hills of Nice".
Bouhlel was identified by fingerprints after his identification card was found in the truck, Molins said. He also said that the attack in Nice is of a "terrorist nature".
There don't appear to be any obvious indications that Bouhlel was radicalized in a French prison or by a radical mosque - neighbors in other media reports suggest he wasn't particularly religious.
But as the last firework fizzled, gunfire rang out - authorities and witnesses say the driver shot from the cab of the truck - and the truck accelerated down the crowded street. The so-called Islamic State group, also known as ISIS or ISIL, claimed responsibility for that attack.
"Investigations are now underway to establish if the individual acted alone or if he had accomplices who might have fled", interior ministry spokesman Pierre-Henry Brandet said.
Hollande declared a national mourning period from Saturday to Monday.
The measure was in place in the wake of the terror attacks in Paris in November, the worst terror attack in the country's history, which left 130 people dead. As many as 60 security and military troops have been killed in recent years.