Four French police staffers were killed in a knife attack by a colleague at the Paris police headquarters on Thursday afternoon, October 3.

The assailant, 45-year-old Mickaël Harpon, went on a rampage and attacked his colleagues before he was shot dead by a junior officer.

Although the motive behind the attack is yet to be determined, the police union initially suggested a workplace dispute was the cause of the deadly attack. However, the police have handed over the investigation to anti-terror detectives “in the light of the evidence gathered by criminal investigators.”

The 45-year-old IT specialist is reported to have converted to Islam about 18 months ago. The police spokesperson, however, said there was no indication that Harpon had been radicalized before Thursday’s attack.

The investigators have since interrogated several people close to the attacker in addition to conducting a search at his home in northern Paris.

Harpon is reported to have entered the building at about noon and stabbed two people on a stairway and three others in two offices.

A woman and three men were killed while a fifth person is being treated after sustaining serious knife wounds.