Nice attacker had expressed support for Islamic State
The truck driver who killed 84 people in Nice had expressed support for the Islamic State group and searched online for information about the attack on a gay nightclub in Orlando.
Paris prosecutor Francois Molins, who oversees terrorism investigations, said attacker Mohamed Lahouaiej Bouhlel had clearly plotted out the Bastille Day attack, with reconnaissance visits to the beach-front area where he mowed down revellers.
Mr Molins described a quick radicalisation of a man who in the past had not been religious. He said a review of Bouhlel's computer and phone showed online searches relating to IS, other jihadi groups and violent images.
IS has claimed responsibility for the attack. Bouhlel's uncle claims his nephew was indoctrinated about two weeks ago by an Algerian member of IS in Nice.
Sadok Bouhlel said his nephew's family problems - he was estranged from his wife and three children - meant the Algerian extremist "found in Mohamed an easy prey for recruitment".
Meanwhile, France held a country-wide moment of silence on Monday to remember the victims, but mourning was punctured by anger and political division.
Crowds massed on the Riviera seafront in Nice booed the visiting Prime Minister Manuel Valls, whose Socialist government is coming under increasing criticism from the public and the conservative opposition for failing to prevent the Bastille Day carnage.
Along the curved, rocky Nice beach Monday, thousands of people gathered to mark the moment of silence, alongside religious leaders from the Muslim, Christian and Jewish communities and other local dignitaries.
A total of 59 people remain in hospital after Thursday's attack, 29 of them in intensive care, out of 308 people injured overall.
At the Pasteur hospital, where many of them are being treated, emergency responders and other medical personnel gathered in the courtyard for the moment of silence, standing still in a row and clapping when it was over.
A sign posted around town demonstrates a strong feeling of solidarity, calling for blood donations, stuffed animals for injured children and a plea to "unite against the crazy ones".
But bitterness is also close to the surface. French Prime Minister Manuel Valls was loudly booed as he arrived at and left the ceremony on the Nice shore.
President Francois Hollande's Socialist administration has come under blistering criticism from opposition conservatives after the attack. Former president Nicolas Sarkozy accused the government of bad policies that he says failed to prevent three major attacks in the past 18 months.
"Everything that should have been done over the past 18 months was not done," Mr Sarkozy said on Sunday night. "We are in war, a total war. Our enemies don't have no taboos, no borders, no principles. So I will use strong words: It will be us or them."
He called for electronic bracelets for anyone suspected of potential radicalisation, and for expelling anyone suspected of possible terrorism links, direct or indirect.
But interior minister Bernard Cazeneuve hit back on Monday, listing a series of laws and extra police forces created under Mr Hollande's presidency "to face a threat that France wasn't prepared for" when he took over from Mr Sarkozy in 2012.
Seven people are in custody in the probe into the Nice attack. Three of the suspects were brought to French intelligence headquarters in Paris on Monday to face eventual terrorism charges, according to a security official.
At the home of one of the suspects, an Albanian national, investigators found 11 telephones, cocaine and 2,600 euro (£2,165) in cash, according to a security official and the Paris prosecutor's office.