A 23-year-old man from the eastern French city of Strasbourg has been identified as the third gunman involved in the attack on Paris's Bataclan music hall, police sources said on Wednesday.
Foued Mohamed Aggad had travelled to war-torn Syria with his brother and a group of friends at the end of 2013, according to a source close to the investigation.
The two other attackers involved in the massacre of 90 concert-goers at the Bataclan - Omar Ismail Mostefai, 29, and 28-year-old former Paris bus driver Samy Amimour - had also been in Syria.
Two of the gunmen blew themselves up with suicide belts packed with explosives after the killing spree, the worst of the November 13 Paris attacks.
The third was shot by police who stormed the venue with hundreds of people still inside.
Most of the group of six men from Strasbourg who went to Syria with Aggad were arrested in the Meinau area of the city on their return in May last year and are all in custody on terrorist charges.
But Aggad stayed on in Syria, the source said.
Others 'killed fighting'
Investigators believe two brothers from the group, Mourad and Yassine Boudjellal, were killed fighting with the Islamic State in Iraq and the Levant (ISIL) before it restyled itself as the Islamic State (IS) group.
When questioned on their return, the men claimed they had been horrified by what they had witnessed in Syria and had started to dribble back to France from February 2014.
They claimed to have gone to Syria for humanitarian work but prosecutors believe they were part of the Islamic State group, which claimed responsibility for the carnage in Paris.
Aggad was identified at the end of last week after his DNA was matched with members of his family, the police source said.
Police suspect the Strasbourg group had been recruited by Mourad Fares, 31, who was known to French intelligence for recruiting jihadist fighters through social media and the Internet.
Fares - who France's Interior Minister Bernard Cazeneuve has described as a "particularly dangerous individual" - was arrested in August 2014 in Turkey before being handed over to the French authorities.
Cazeneuve said he was an important link-man between various "jihadist terrorist movements," including the IS group and Al-Qaeda's Syrian affiliate Al-Nusra.
Nearly 1,500 people were watching the Californian band Eagles of Death Metal play at the Bataclan when the gunmen burst in last month, leaving 90 dead and hundreds hurt, mostly people under 40.
The band made an emotional return to the venue on Tuesday, with lead singer Jesse Hughes in tears as he laid a single flower among the piles of tributes to the dead.
The band's merchandising manager, Nick Alexander, a 36-year-old Briton, was among the victims.
The Bataclan's owners have said they want to reopen the hall at the end of next year and the Eagles of Death Metal say they want to play in the first concert.