PARIS • Investigators combed an IT staff member's computer yesterday for clues as to why he stabbed four colleagues to death at police headquarters in Paris, as his wife said he had been "agitated" before going on the rampage with a kitchen knife.

The 45-year-old killed three men and a woman - three police members and an administrative staff - in a frenzied 30-minute attack that ended when he was shot in the head.

Two others were injured in the lunchtime stabbing spree that sent shock waves through an embattled force already complaining of low morale.

The attacker's wife told investigators that her husband, who had a severe hearing disability, had displayed "unusual and agitated behaviour" the night before his crime, a source close to the investigation told Agence France-Presse.

A search of the couple's house in a low-income Paris suburb near the Charles de Gaulle airport found no evidence that the man, who converted to Islam about 18 months ago, had been driven to his criminal deed by radical religious ideology, the source added.

Computer equipment seized in the search was being examined yesterday, the source said.

The man, born in the French Caribbean territory of Martinique, was employed as a computer scientist in the intelligence branch at police headquarters, right next to the Notre-Dame cathedral in the historic heart of Paris. He had worked there since 2003 until Thursday, when he committed the deadliest attack on police in France in years.

Shortly after the killings, Paris prosecutor Remy Heitz said anti-terror investigators were not involved in the murder probe.

All possible motives were being examined, sources said on Thursday, including the scenario of a personal conflict at work.

"He was a very quiet person. I used to see him going to the mosque but he practised (his religion) in a normal way," a neighbour, who asked not to be named, told AFP.

Locals said the man had two children aged three and nine.

Interior Minister Christophe Castaner said on Thursday that the assailant had "never shown any behavioural problems".

The man had used a kitchen knife to stab two policemen and a male administrative colleague in two offices on the first floor of the building, before attacking two women on the staircase on his way to the courtyard outside.

One was a police officer who died at the scene. The other, an administrative worker, was seriously injured.

The assailant wounded another policeman in the courtyard before he was shot in the head by a colleague, sources told AFP.

The lives of the two wounded colleagues are not in danger, a source said yesterday.

Thursday's killings came amid growing tensions within the ranks of the police, stretched to the limit after months of containing weekly "yellow vest" anti-government demonstrations, and years of high alert following a string of terror attacks in France.

The police have also been a recurring target of extremist groups, such as the Islamic State in Iraq and Syria, behind a wave of attacks since 2015 - from large synchronised assaults to isolated knife and gun attacks.

AGENCE FRANCE-PRESSE