The suspected gunman, 29-year-old Mehdi Nemmouche, was arrested Friday in the southern French city of Marseille in possession of a Kalashnikov rifle and a handgun similar to the ones used in the attack on May 24, the sources told AFP.
He has been detained on suspicion of murder and attempted murder in connection with a terrorist enterprise, a judicial source said.
The shooting by a lone gunman killed three people outright -- an Israeli couple and a Frenchwoman, while the fourth victim, a 24-year-old Belgian man, was left clinically dead.
Customs officials detained Nemmouche at Marseille's coach station on board a bus arriving from Amsterdam via Brussels.
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According to sources close to the investigation, he was carrying a Kalashnikov automatic rifle and a gun with ammunition in his luggage, as well as a miniature video camera.
Originally from Roubaix in northern France, he is believed to have travelled to join Islamist fighters in Syria in 2013, and was known to the French domestic intelligence agency DGSI, the source said.