PARIS — The suspect in a deadly knife attack at Paris police headquarters worked for more than 15 years in the complex as he began following a “radical vision” of Islam, a top prosecutor said Saturday amid tense political fallout from the incident.

French prosecutors are now investigating Thursday’s attack that killed four people – two police officers and two headquarters staff – as an act of terror.

But opposition leaders have accused the French government of incompetence for delays in identifying the apparent motives of the suspect, a 45-year-old man identified as Mickaël Harpon who was killed at the scene by a police intern.

Initially, French authorities were hesitant to label the attack as possible terrorism. That cautious approach also has drawn fiery opposition backlash against the French Interior Ministry – including calls for Christophe Castaner, France’s interior minister, to resign.

Hours after the attack, Castaner told reporters at the scene that the Harpon had “never presented behavioral difficulties, nor the slightest sign of alarm.”

But France’s anti-terrorist prosecutor, Jean-Francois Ricard, offered a starkly different portrait in a news conference Saturday.

Ricard said Harpon, who had worked as a computer specialist at the police headquarters since 2003, had been in contact with individuals associated with the “radical Salafist movement,” had converted to Islam roughly a decade before, and “adhered to a radical vision of Islam.”

Harpon exchanged 33 text messages with his wife on Thursday morning that had an “exclusively religious connotation” and ended with “Allahu akbar,” or “God is great” in Arabic, Ricard said.

He also confirmed earlier reports circulating in French media that the suspect had previously said he understood the motives behind the January 2015 attack on the offices of the satirical newspaper Charlie Hebdo, where two Islamist gunmen killed 12 people.

For now, much of the outrage from Thursday’s stabbings has focused on Castaner and his initial statements.

“Either he knew, and it’s a state scandal, or he didn’t know, and it shows his total incompetence,” Eric Ciotti, a lawmaker with the right-wing Les Républicains party, wrote on Twitter. “Which French citizen can think that the Interior Ministry is ensuring his protection with Castaner at its head?”

Similar statements emerged from France’s significantly weakened Socialist party, although most in this camp stopped short of calling for Castaner’s resignation.

“The latest information suggests that there has been, at the least, a certain amateurism in the recruitment of Police Prefecture agents and that the information that should have been given was not,” David Habib, a Socialist parliament member, told Le Monde newspaper.

The suspect used a metal kitchen knife and an oyster knife – apparently purchased at a nearby shop half an hour before the attack during his lunch break, officials said.

“The autopsies attest to a scene of extreme violence,” Ricard said.

Harpon fatally attacked two colleagues in his office, then fatally stabbed another colleague in an office nearby on the same floor, Ricard said. On the staircase toward the ground floor, Harpon then fatally stabbed another officer and seriously injured an administrative assistant, whose condition is no longer critical.

He was then shot and killed by a 24-year-old intern.

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