Dekhar apparently tried to kill himself before he was arrested Wednesday, Valls told reporters early Thursday.
Agnes Thibault-Lecuivre, a spokeswoman for the French prosecutor's office, said the suspect was arrested in an underground parking lot in Bois-Colombes, 10 kilometers (6 miles) north of Paris. She and police union official Christophe Crepin said the man appeared heavily medicated when he was detained.
"My colleagues noticed he was not very lucid. They deduced that he had taken medicines, because of the capsules nearby. They called the ambulance, which brought him to the hospital. There he is incarcerated but in a medical environment," Crepin told The Associated Press.
Dekhar was found after a witness reported to police that a suspect resembling images broadcast on national television since Monday had stayed at his house in recent days, said Paris judicial police chief Christian Flaesch.
Authorities had released video footage and photos of the shooter, who was wielding a pump-action shotgun in the attacks on Liberation and BFM.
The gunman entered the lobby of Liberation around 10 a.m. Monday and opened fire. A 23-year-old photographer, who works at the paper as a freelance assistant, was in intensive care after being shot near the heart and in the arm. Valls said he visited the photographer Wednesday and he's "doing better."
Soon after the shooting at Liberation, three shots were fired in front of the headquarters of the bank Societe Generale in the Paris suburb of La Defense. No one was hurt.
Less than an hour later, a man called police to say he had been taken hostage by a gunman in the town of Puteaux, next door to La Defense. Police said the gunman forced his hostage to drive six kilometers (3 1/2 miles) back toward central Paris, then let him go on the Champs-Elysees.
Three days before at BFM-TV, an armed man threatened journalists with a shotgun in the news network's lobby before fleeing.
He left behind unused cartridges, and told witnesses, "Next time, I won't miss," according to authorities. It was unclear whether the gunman's weapon malfunctioned or whether he chose not to shoot.
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Angela Charlton in Paris contributed to this report.