The office announced the decision in a two-line statement and provided no details about the evidence that persuaded prosecutors a terror investigation was warranted. David Le Bars, head of the Union of National Police Commissioners, told French broadcaster BFM TV it came from easily accessible sources found in a search of the attacker's home.
"We knew that searching through his computer histories, the websites visited, his relations, we would quickly have some information," Le Bars said. He called the suspicion the slayings of three police officers and an administrator resulted from an extremist plot "a cataclysm" since the attacker worked for the police department. A fifth person was seriously injured.
The 45-year-old employee worked as a technology administrator in the Paris police intelligence unit. Investigators scoured the man's computer and cellphone Friday for clues to his motive. They also interviewed witnesses and his wife, who was taken into custody Thursday, said a police official who spoke on condition of anonymity to discuss the ongoing investigation.
The wife told police her husband, who was deaf, had visions and made incoherent statements during the night before the attack BFM TV and France Info reported. The French government said Friday morning there was nothing to suggest the armed attacker had any ties to extremist groups.
Prosecutors issued the statement about the investigation in the afternoon, three hours a news conference where Paris police chief Didier Lallement made no mention of possible extremist links, saying only, "We don't rule out any hypothesis at this stage."
Authorities said the attacker had worked for the Paris police force since 2003, didn't have a history of psychiatric problems, and converted to Islam 18 months ago. At the news conference Friday, Lallement said the rookie officer who shot the stabber completed police academy training six days before the attack.
Assigned to security duty at the large police compound across the street from Notre Dame Cathedral, the rookie ran into the courtyard to counter the attack and confronted the 45-year-old administrator, Lallement said.
The police force held a minute of silence in the same courtyard on Friday morning. "We've been hurt at the heart, but we are still standing," the police chief said. __ Nicolas Vaux-Montagny contributed to the story.