PARIS — The man who killed 84 people in a terrorist attack in Nice, France, last week planned his assault over several months and got help from at least five people, the Paris prosecutor said on Thursday.
However, although the Islamic State called the attacker one of its “soldiers,” there is as yet no evidence that he or the suspected accomplices had any direct contact with the terrorist network, according to the prosecutor, François Molins, who handles terrorism investigations in France.
At a news conference in Paris, Mr. Molins announced that he had opened a formal investigation into multiple charges, including participation in a criminal terrorist conspiracy, terrorist murder, attempted terrorist murder, and illegal weapon possession and transportation.
The attacker, Mohamed Lahouaiej Bouhlel, a 31-year-old Tunisian who lived in Nice, drove a cargo truck through crowds that had gathered on the city’s waterfront promenade to watch Bastille Day fireworks on July 14. He also fired an automatic pistol at the police, before they shot and killed him.
Mr. Molins said that investigators had been able to confirm “not only the premeditated character of Mohamed Lahouaiej Bouhlel’s deadly act” but also that he had “benefited from support and complicity in the preparation and carrying out of his criminal act.”
Like Mr. Lahouaiej Bouhlel, none of the accomplices were known to French intelligence services, Mr. Molins said. They will be presented before a judge to be formally handed preliminary charges later on Thursday, Mr. Molins said.
The five accomplices were arrested in the days after the attack.
Mr. Lahouaiej Bouhlel’s estranged wife was also arrested, but was released without charges on Sunday, as was a man who had been wrongly identified as a suspect, according to Audrey Delaunay, the man’s lawyer.
Questions continued to be raised about security measures in Nice on the night of the attack, which killed not only French citizens who had been celebrating their national holiday, but also people of 19 other nationalities, including citizens of Algeria, Brazil, Estonia, Kazakhstan, Madagascar and the United States.
France’s Socialist government has sparred repeatedly with opposing politicians on the right and far-right, especially local officials in Nice, over how many national and municipal officers were securing the promenade on the night of the attack and how they were spread out. The national police answer to the state, whereas municipal officers answer to city authorities.
The newspaper Libération reported on Thursday that only one municipal police car was positioned at the spot where Mr. Lahouaiej Bouhlel barreled through and on to the promenade, and it said that although state and city officials had agreed on — and stuck to — a security plan for Bastille Day, the government had misrepresented those measures after the attack.
The interior minister, Bernard Cazeneuve, who accused the newspaper of using “conspiracy theory” methods, has ordered an internal police investigation, separate from the ongoing judicial one, which will look into the Bastille Day security measures in Nice.
Questions have also been raised about why the authorities did not position heavy obstacles at the entrances to the promenade’s pedestrian area, to block vehicles from entering.
The authorities across France are rushing to strengthen security at the dozens of events held around the country over the summer.
In Paris, the authorities have added vehicle barriers at Paris Plages, an annual event that started on Wednesday where sections of the Seine’s embankments are turned into artificial beaches, but have canceled other events, like an open-air film festival and a pedestrian day on the Champs-Élysées.
On Thursday, the French Parliament also passed a bill extending for another six months the state of emergency that was declared after the November attacks that killed 130 people in and around Paris.
The latest extension runs until the end of January. If carried out to its term, it will set a record in France for uninterrupted time spent under a state of emergency, which grants French authorities extraordinary policing powers, such as the ability to carry out police raids or place people under house arrest without a judge’s authorization.
The bill passed on Thursday also added new emergency powers, such as the ability for the police to seize computers and phones and copy the data on them during such a raid, and it strengthened several antiterrorism measures that are not directly related to the state of emergency, such as the ability for state officials to place a person returning from Syria or Iraq under house arrest for up to three months instead of one.
A parliamentary report from earlier this month on intelligence and security failings before the January and November attacks in France last year found that the state of emergency was “useful” but “limited” to fight against terrorism.
The report, published this month by a bipartisan parliamentary committee, noted that the state of emergency had enabled the authorities to quickly disrupt and gather intelligence on criminal or terrorist networks in the immediate aftermath of the Nov. 13 attacks, but that it was no longer as effective once the element of surprise had faded.
Separately, a lawyer in Nice attempted to commit suicide on Wednesday after it emerged that he had lied about being Mr. Lahouaiej Bouhlel’s counsel in a former case. Several news organizations, including The New York Times, had described the lawyer, Corentin Delobel, as having represented Mr. Lahouaiej Bouhlel. The head of the local bar association told the newspaper Nice Matin that Mr. Delobel would face disciplinary measures.