French police are holding a man on suspicion he opened fire with a shotgun at the offices of a left-wing newspaper and a major bank in Paris, judicial sources said on Wednesday.
The suspect was arrested in the evening in his car in the parking lot of a Paris suburb, one source said.
A second source said the man was thought to be under medication and was not in a state to be questioned immediately, but police were testing his DNA against traces found on cartridges left behind by the gunman.
The gunman seriously wounded a 23-year-old photographer's assistant in the lobby of the Liberation newspaper on Monday before fleeing.
Shortly afterwards, he fired at least three shots into the lobby of the headquarters of Societe Generale in the La Defense business district. There were no casualties.
The gunman later vanished into the crowds of Paris' Champs-Elysees boulevard after forcing a driver at gunpoint to take him there.
With a vast manhunt under way, police have received hundreds of tip offs from the public after circulating photographs from security cameras, including some of his face.