Paris (CNN) The investigation into a knife attack that left four people dead at Paris police headquarters has been forwarded to French terrorism prosecutors, a source at the Paris prosecutor's office told CNN Friday.

Three policemen and a female police administrative worker were killed Thursday by a fellow member of staff, who was later shot dead inside the building located near Notre Dame Cathedral on the Île de la Cité in central Paris.

French Interior Minister Christophe Castaner said the assailant was a 45-year-old man who had been an employee at the police station since 2003.

On Thursday, a source in the Paris prosecutor's office told CNN that the wife of the attacker had been taken into custody. It was not clear if she was at the scene of the attack or why she was taken into custody.

Police block the street after the knife attack.

President Emanuel Macron, accompanied by Prime Minister Edouard Philippe and Castaner, visited the scene Thursday.

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