The man who killed 84 Bastille Day revellers in the French city of Nice by driving a truck at a crowd had been radicalized recently and quickly, France's Prime Minister told a newspaper as a further 18 victims fought for their lives on Sunday.
Thursday night's attack at peak holiday time on the Riviera plunged France into new grief and fear just eight months after jihadi gunmen killed 130 people in Paris.
French Health Minister Marisol Touraine said the 18, including one child, were in a critical condition, while about 85 people in total were still hospitalized.
The attacks, along with one in Brussels four months ago, have shocked Western Europe, already anxious over security challenges from mass immigration, open borders and pockets of Islamist radicalism.
Authorities have yet to produce evidence that the 31 year-old delivery driver, Tunisian Mohamed Lahouaiej Bouhlel, shot dead by police, had any actual links to Islamic State. The Islamist militant group claimed the attack though, and Valls said there was no doubting the assailant's motives.
"The investigation will establish the facts, but we know now that the killer was radicalized very quickly," Prime Minister Manuel Valls said in an interview with newspaper Le Journal du Dimanche.
As of Sunday no evidence had been produced to show how he underwent that rapid transformation from someone with no apparent interest in religion.
Relatives and friends interviewed in Nice painted a picture of a man who at least until recently drank alcohol, smoked marijuana and according to French media even ate pork, behaviour that would be unlikely in a devout Muslim.
A report in the Nice Matin newspaper on Sunday said investigators had found no radicalization material in his flat, although they were still looking at his telephone and his computer.
Speaking from his home town in Tunisia, Bouhlel's sister told Reuters he had been having psychological problems when he left for France in 2005 and had sought medical treatment.
As authorities were trying to better understand his motives, two more people, a man and a woman close to Bouhlel, were arrested in Nice early on Sunday.
Three others arrested previously were still being held, but Bouhlel's estranged wife was released without charges after being held since Friday.
The Amaq news agency affiliated with the militant Islamist group said on Saturday in claiming the attack that Bouhlel "was one of the soldiers of Islamic State".
The group, which is under military pressure in its Irag and Syria strongholds from forces opposed to it, considers France a key target given its military operations in the Middle East, and also because it is easier to strike than the United States, which is leading a coalition against it.
France is also home to Europe's biggest Muslim population, and has been criticized in some quarters for fostering racial, ethnic and religious disharmony through its strict adherence to a lay culture that allows no place for religion and ethnicity in schools and civic life.
Long and open borders with neighbouring countries also make it an easy target for attackers who want to melt away afterwards.
Valls defended France's record on attacks, saying security services had prevented 16 over three years and said the group's modus operandi of cajoling unstable people into carrying out attacks with whatever means possible was difficult to combat.
"Daesh gives unstable individuals an ideological kit that allows them to make sense of their acts...this is probably what happened in Nice's case," Valls said, referring to the Arabic acronym for Islamic State.
Despite mounting criticism from the conservative opposition and the far-right over how President Francois Hollande's Socialist government is handling security, Valls said there was no such thing as zero risk and that new attacks would occur.
"I've always said the truth regarding terrorism: there is an ongoing war, there will be more attacks. It's a difficult thing to say, but other lives will be lost."