As thousands gathered in central Paris in mourning and solidarity, authorities in at least five European countries scrambled to tie together leads and hunt down possible accomplices.
Security sources said one of the three brothers died in the Bataclan concert hall where the worst of the bloodshed took place, while another had been detained along with six other people in Belgium.
Seven gunmen wearing suicide belts died during the attacks, which have been claimed by the Islamic State group -- either at the Stade de France stadium, or in and around the Bataclan venue.
Prosecutors say they believe three groups of attackers were involved in the Paris carnage, raising the possibility that one group may still be at large.
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It is now known that three of the suicide bombers were French nationals, but two of the men had lived in the Belgian capital Brussels.
Two cars used in the attacks were hired in Belgium. One was quickly found near the Bataclan venue, and one overnight yesterday in the suburb of Montreuil east of Paris, with two AK47 rifles inside.
The first attacker to be named by investigators is Omar Ismail Mostefai, a 29-year-old father and French citizen, who was identified from a severed finger among the carnage at the Bataclan, where 89 people were killed after heavily armed men in wearing explosives vests stormed into the venue.
Police detained six people close to Mostefai, including his father, brother and sister-in-law, judicial sources said.