The fugitive Strasbourg man suspected of shooting people as he shouted "Allahu Akbar" at the French city's Christmas market is a criminal who turned radical Islamist in jail, officials said.
A manhunt is continuing today for the suspect, identified by authorities as 29-year-old French citizen Cherif Chekatt.
He has 27 criminal convictions for theft and violence, officials said, and has spent time in French, German and Swiss prisons.
Now police are seeking him as the suspect who killed two people, and seriously injured several more last night. Police today released photographs of Chekatt as the hunt continues.
Neighbours believed that Chekatt's brother was a radicalised Muslim, but they remember the suspect as an ordinary local guy.
However to security agencies, Chekatt had represented a potential threat for some time, his beliefs hardened behind bars.
Paris prosecutor Remy Heitz said the suspect shouted out "Allahu Akbar" during the attack.
"Considering the target, his way of operating, his profile and the testimonies of those who heard him yell 'Allahu Akbar', the anti-terrorist police has been called into action," Mr Heitz said.
Interior Minister Christophe Castaner said the gunman had evaded a police dragnet and was on the run, raising concerns of a follow-up attack.
The mother, father and two brothers of the suspect are being held in custody for questioning, said sources close to the investigation.
"The government has raised its security threat to the highest level and is bolstering border controls," Mr Castaner told a late-night news conference.
"We will also reinforce security at all Christmas markets to prevent copycat attacks."
With France still on high alert after a wave of attacks commissioned or inspired by self-styled Islamic State militants since early 2015, the counter-terrorism prosecutor opened an investigation.
Mr Castaner said the gunman exchanged shots with security forces twice as he escaped.
His whereabouts now were unknown, and elite commandos and helicopters were involved in the manhunt.
The Paris prosecutor said the motive for the attack was not known. No-one immediately claimed responsibility, but the US-based SITE Intelligence Group, which monitors jihadist websites, said Islamic State supporters were celebrating.
The attack began at about 8pm as stallholders prepared to close down and restaurants filled in the city, which sits across the Rhine River from Germany. Bystanders were swiftly ushered into nearby shops.
"There was confusion initially but they locked the front doors pretty soon after the gunshots," said US citizen Elizabeth Osterwisch, who was sheltering on the top floor of the Galeries Lafayette department store.
"They moved us several times, eventually settling on the place with the most protection."
MEP Emmanuel Maurel said he had heard the shots and the European Parliament, which is sitting in Strasbourg this week, was put into lockdown.
On the opposite side of the River Rhine, German police also tightened border controls, officials said.
European Commission President Jean-Claude Juncker tweeted: "My thoughts are with the victims of the Strasbourg shooting, which I condemn with the utmost firmness. Strasbourg is an excellent symbol of peace and European Democracy. Values that we will always defend."
European security agencies have feared for some time that Islamist militants who left Europe to fight for the so-called Islamic State in Syria and Iraq would return after the jihadist group’s defeat, with the skills and motivation to carry out attacks at home.
There have also been attacks in Paris on a policeman on the Champs-Elysees, the offices of satirical weekly publication Charlie Hebdo and a kosher store.