The man who stabbed two young women to death in Marseille in an attack claimed by the Islamic State group used seven different identities and had been arrested just days earlier, French prosecutors said on Monday.
Authorities said the killer, who was shot dead by anti-terror troops after Sunday's attack outside the southern city's main train station, had used a Tunisian passport last week under the name of a 29-year-old with the first name Ahmed.
But investigators are seeking to confirm his identity as the attacker -- who had a history of petty crime but was not on a jihadist watch list -- used seven aliases, anti-terror prosecutor Francois Molins told reporters in Paris.
Molins said "the method of the attacker" was in line with calls from the Syria-based terror group to followers in the West to strike vulnerable targets, such as train stations.
The IS group's propaganda agency Amaq claimed the killer was one of its "soldiers", but a source close to the investigation told AFP no solid evidence linked him to the jihadists.
The attack in France's second-biggest city followed a string of stabbings around Europe claimed by or blamed on radicals.
The man killed two 20-year-old cousins, one of them a "brilliant" medical student who was studying in the city, according to Aix-Marseille University chief Yvon Berland.
Her cousin, a nursing student from the eastern city of Lyon, was visiting her for the weekend.
Molins confirmed that witnesses heard the attacker shout "Allahu Akbar" as he lunged at the women with a 20-centimetre knife before threatening soldiers, who shot him dead.
The attacker's fingerprints showed he had had seven brushes with the law since 2005 -- most recently when he was arrested last Friday in Lyon for shoplifting.
He presented the Tunisian passport to police, saying he was divorced, used "hard drugs", and had no fixed address.
The shoplifting charges were dropped for lack of evidence, and local authorities "were not able to take a decision to deport him," Molins added.
Police evacuated Marseille's ornate Saint Charles station after the attack, temporarily halting all train traffic on some of France's busiest lines.
"I was on the esplanade just in front of the station," Melanie Petit, an 18-year-old student, told AFP. "I heard someone shout 'Allahu Akbar' and I saw a man who seemed to be dressed all in black."
French President Emmanuel Macron tweeted on Sunday that he was "deeply angered by this barbaric act".
The attack comes as parliament prepares on Tuesday to vote on a controversial anti-terror bill that transfers some of the exceptional powers granted to police under a 22-month-old state of emergency into national law.
France has been under a state of emergency since the IS gun and bomb attacks in Paris in November 2015 -- part of a string of jihadist assaults that have left more than 240 people dead over the past two years.
But critics warn that making parts of the state of emergency permanent would give police too much free rein, undermining freedoms in a country seen as a beacon for human rights.
Knives have been the weapon of choice in a string of smaller-scale attacks in recent months, mainly targeting troops from the 7,000-strong Sentinelle anti-terror force set up to patrol the streets and vulnerable sites such as stations and tourist attractions.
In most cases, the attackers were shot dead at the start of their rampage, before they could kill others.
The Marseille attack came only days after IS released a recording of what it said was its leader Abu Bakr al-Baghdadi urging his followers to strike their enemies in the West.
The French government has deployed troops and its air force to the Middle East and is a leading partner in the US-led international coalition fighting IS in Iraq and Syria.