The man responsible for Thursday’s murderous attack in Nice was a violent petty criminal unknown to the French security services, who was born in Tunisia but had been living and working in the coastal city, prosecutors have said.

Mohamed Lahouaiej-Bouhlel, a 31-year-old delivery driver and father, was shot dead by police after killing 84 people, including 10 children and teenagers, and injuring scores more in a deadly Bastille Day rampage.

Despite a criminal record dating from his first conviction in March this year, Lahouaiej-Bouhlel was not known by French or Tunisian officials to have links to terrorist organisations and was said by neighbours to have had little apparent interest in religion.

Echoing the remarks of French officials, security sources in Tunisia said he was not known by the Tunisian authorities to hold radical or Islamist views.

At a packed press conference, the Paris prosecutor François Molins said Lahouaiej-Bouhlel had been “completely unknown to both France’s domestic and foreign intelligence officials”. But he added: “Although yesterday’s attack has not been claimed, this sort of thing fits in perfectly with calls for murder from such terrorist organisations.”

Molins said the investigation would focus on a number of key issues, including potential accomplices, how Lahouaiej-Bouhlel had procured the gun he fired at police and whether he was connected to radical jihadi networks.

Later on Friday, French prime minister Manuel Valls said that although he could not confirm the attacker’s motives, Lahouaiej-Bouhlel “is a terrorist probably linked to radical Islam one way or another”.

On Friday, at the modest five-storey block of flats in the Quartier des Abattoirs where he had lived and which was raided by officers from the elite RAID unit at 9.30am,neighbours described him as a quiet and “not very religious” man.

Born in 1985 in Tunisia, Lahouaiej-Bouhlel had come from the town of M’saken near the city of Sousse – where dozens of foreign tourists were shot dead on a beach last year – and had reportedly last visited the town four years ago.

On Friday night his father told Agence France-Presse that his son had suffered from depression.

“From 2002 to 2004, he had problems that caused a nervous breakdown. He would become angry and he shouted … he would break anything he saw in front of him,” Mohamed Mondher Lahouaiej-Bouhlel said outside his home in M’saken. He said he was prescribed medication to treat his depression.

He said they had heard nothing from him after he left for France. He also agreed that he had little to do with religion. “He didn’t pray, he didn’t fast, he drank alcohol and even used drugs,” he told AFP.

Speaking to reporters in his apartment building, neighbours said he had rarely spoken to them and did not return greetings when their paths crossed in the working-class neighbourhood. Photographs from inside the flat showed a cramped and shabby home whose contents had been turned over by investigators.

Sebastien, a neighbour who spoke on condition that his full name was not used, said Lahouaiej-Bouhlel did not seem overtly religious, often dressed in shorts and sometimes wore work boots.

He had a van parked nearby and owned a bike, which he brought up into his first-floor apartment.

Of those who were interviewed, only one, a neighbour on the ground floor, said she had had any concerns about him – describing him as “a good-looking man who kept giving my two daughters the eye”. Other people who knew him – quoted in the French media – described an individual interested in women and salsa music.

Another neighbour, identified only as Jasmine, aged 40, told the Guardian: “He was quite handsome, greyish hair, looked a bit like George Clooney. He never answered when we spoke or said hello, he just sort of stared at us aggressively.

“I was really scared of him. All I knew is that he had trouble with his wife, but we never saw her or their kids. He spent a lot of his time at a bar down the street where he gambled and drank.”

Others who knew him said they believed he was either divorced or in the process of getting divorced. Police raided the 12^th-floor apartment of his estranged wife, elsewhere in the city, where neighbours said he had not lived for three years. His wife was later taken in for questioning.

In the cluster of towering red and white blocks of social housing in northern Nice, where the couple had lived together years earlier, the Muslim community was in shock. A group of teenagers sitting on the porch of one of the huge towers claimed that Lahouaiej-Bouhlel, who they said had been in conflict with his ex-wife, drank, smoked and never visited the mosque.

“I was woken up by people screaming: ‘Let her go, she didn’t do anything’,” said one woman, who gave her name as Saïda, when asked about the questioning of his ex-wife. “It hurts because they are an adorable family and I don’t think they have anything to do with it. We knew her husband was violent and had moved out a while ago but that is all.”

Another woman, Halima, added: “We are all really stunned. All those victims. We didn’t sleep all night and we cried for absolutely everyone.” The group lost a friend, who they said was the first person to be hit by the driver on Thursday night.

The first clues to Lahouaiej-Bouhlel’s identity emerged in the immediate aftermath of the attack as police combed through the bullet-ridden lorry he had rented from a local company on 11 July. Investigators recovered a mobile phone, bank card and driver’s licence – all pointing to Lahouaiej-Bouhlel.

Known to the police for a violent altercation in which he had hurled a wooden pallet at another driver, Lahouaiej-Bouhlel was given a suspended sentence and asked to contact police once a week, which he did, said the French justice minister, Jean-Jacques Urvoas.

But little else in Lahouaiej-Bouhlel’s past indicated he would commit an atrocity on the scale of Thursday’s attack. Investigators will want to know where he acquired the stash of weapons found in the cab of the truck, whether he was indeed acting alone or had accomplices – and, perhaps above all, what motivated him to launch his murderous assault.

In practical terms, too, police will have questions to answer, including how – amid a high-level security alert and state of emergency – he was able to get through a security perimeter to launch his attack.

One of a community of 40,000 Tunisians living in Nice – among a wider community of 120,000 in the Provence-Alpes-Côte d’Azur region – he was not, say neighbours in the Quartier des Abattoirs, a familiar figure in the 18 or so mosques in the city.

One focus of the investigation is likely to be connections in Nice itself – a city which has in recent years emerged as a centre of radicalisation and jihadi recruitment, not least through the network of Omar Omsen, also known as Oumar Diaby, whose name has repeatedly surfaced in French counter-terrorism investigations.

Peter Beaumont and Sofia Fischer in Nice