The man, aged between 35 and 40, took a cardriver hostage after firing shots outside the headquarters of the Société Générale bank at Paris's La Défense business district, forcing him at gunpoint to drive him to the Champs Elysées.
He said that he had just come out of prison, was "ready for anything" and had a grenade, the driver told police, according to sources.
He was also armed with the pump-action shotgun that he used outside the bank and at the office of Libération newspaper, where he seriously injured a 23-year-old photographer who had arrived for his first day of work as a freelancer at the daily.
The victim's condition had slightly improved on Tuesday morning, although it was still critical.
Police have distributed new photographs of the gunman, who appears to be the same man who attacked the offices of the BFMTV channel on Friday, taken by CCTV on a tramline station at La Défense.
Despite over 400 calls from the public, police have still not identified him, although CCTV footage have allowed police to establish that he is white, of average height, was wearing glasses and had a pepper-and-salt beard.
BFMTV editor-in-chief Philippe Antoine came face-to-face with the man on Friday and described him as "very precise in his movements, not panicked at all".
Police were stationed outside media offices and at Paris metro stations on Tuesday morning and on alert elsewhere in France.
Libération defiantly declared "We will continue" in its Tuesday edition and devoted four pages to the incident, quoting a staff member as saying, "It lasted no mre than 10 seconds, any one of us could have been hit."