The Tunisian who drove a truck through a crowd, killing 84 people on the Nice Riviera in France on Bastille Day (July 14) "could have been influenced by religion," his former lawyer said.

Corentin Delobel defended Mohamed Lahouaiej-Bouhlel in court on assault charges earlier this year, CNN reports.

At that time Delobel said he saw no signs that Bouhlel had been radicalised. He now regrets that his defence of him prevented the suspect from being jailed, which would have prevented him from carrying out his planned mass murder.

"I told myself I did my job. But if I had done my job badly, he might be in prison, and he may have never done what he did," he said.

Instead, the 31-year-old suspect was meted only a six-month prison sentence for violence with a weapon.

Delobel described Bouhlel, who was born in Tunisia but had a permit to live and work in France, as someone who "wasn't very intelligent" but said he "could have been influenced by religion" in carrying out the attack.

He said Bouhlel was a heavy drinker who had a history of abusing his wife and was "very much the stereotype of a petty criminal."

"There was nothing that would have suggested in reality he was a jihadist," he said.

French Interior Minister Bernard Cazeneuve said it seemed that the suspect "became radicalised very quickly."

Police shot and killed Bouhlel after he plowed the truck he was driving through a crowd on the Promenade des Anglais for a mile. More than 200 were injured in the attack.

An Albanian couple were also arrested by French authorities on Sunday. Six people are currently in custody over the attacks.

Bouhlel's wife was arrested at her apartment on Friday but was released on Sunday without any charge. Her lawyer, Jean-Yves Garino said the woman, who has three kids with Bouhlel, had not been in contact with the suspect since they were in the middle of a divorce case.

On Monday, Cazeneuve said any link between Bouhlel and the Islamic State (ISIS) had "yet to be established" although ISIS was quick to claim that it was responsible for the attack.

"What we want to know now is what were the links between the man who was behind this dreadful attack and the terrorist networks," Cazeneuve said, according to RTL France. "Those links, for the moment, have yet to be established by the investigation. So we must still be prudent with what we say on that subject."

Prosecutor Francois Molins said Bouhlel searched online for terrorist propaganda days before the attack. His personal computer revealed photos of dead bodies and fighters holding the ISIS flag.

"If no element at this stage shows the allegiance of Mohamed Lahouaiej Bouhlel nor links with individuals claiming to be from (ISIS), the use of his computer, as I've just detailed to you, illustrates an interest and, at this stage, we can say recent investigations into the jihadist radical movement," Molins said.