The civilian police worker who slaughtered four colleagues in a frenzied knife attack adhered to 'a radical vision of Islam' an anti-terror prosecutor said.

The assailant, 45-year-old computer expert Michael Harpon, had been in contact with members of the 'Salafist Islamist movement', prosecutor Jean-Francois Ricard told reporters.

The attacker 'agreed with certain atrocities committed in the name of that religion' and defended the Charlie Hebdo attacks in 2015 which rocked Paris, Ricard said.

He had also changed his attire in recent months and wished to no longer 'have certain kinds of contact with women'.

Men in balaclavas walk outside the building in Gonesse where Michael Harpon lived after the knife attack on Thursday which killed four

Military personnel block the bridge near Paris Police headquarters after the knife rampage

Three police officers and an administrative worker - three men and a woman - died in the frenzied 30-minute attack on Thursday at the police headquarters, a stone's throw from the Notre-Dame cathedral in the historic heart of Paris.

The assailant was eventually shot dead by police.

Two other people were injured in the Thursday lunchtime stabbing spree that sent shock waves through an embattled French police force already complaining of low morale.

Sources at the Paris prosecutor's office said on Friday the case had been passed to the anti-terrorist prosecutor's office PNAT after early enquiries suggested that the attacker, a convert to Islam, could have become radicalised.

Michael Harpon, 45, was shot dead following the rampage inside the historic Paris Police Prefecture, next door to Notre Dame Cathedral

Police cordon off a road near the site of the massacre, with Notre Dame cathedral - currently closed after the fire in April - seen in the background

The assailant was born on the French overseas territory of Martinique in the Caribbean.

Sources said he had worked in a section of the police service dedicated to collecting information on jihadist radicalisation.

Several people interviewed by police have since revealed he converted to Islam in 2008, not 18 months ago as had been suggested, according to BFMTV.

Harpon also had links with a hate preacher in the Val-d'Oise who is known to French intelligence agencies, investigators found after searching his phone.

They also found texts between Harpon and his wife shortly before the attack which mentioned the 33cm ceramic knife.

Iham replied, 'Only God will judge you, Allahu akbar', according to Le Parisien.

The attack took place at the Paris police headquarters in the historic centre of the city, near the fire-ravaged Notre Dame cathedral

People console each other on their way out of Paris police headquarters after the force's worst loss of life in a single day since World War II

Iham, who was arrested shortly after the attack, told detectives that Harpon had 'heard voices' and was 'incoherent and suffered a dementia attack' the night before.

Following a raid on the couple's flat in the Paris suburb on Gonesse, anti-terrorist prosecutors in the French capital have opened an enquiry for 'assassination of a public servant in relation to a terrorist enterprise, attempted assassination of a public servant in relation to a terrorist enterprise, and conspiracy in terrorism'.

Computer records and telephone intercepts have also linked Harpon to a 'radical Islamist group' such as ISIS of Al-Qaeda, said a source close to the case.

Iham Harpon remains in custody, and is also believed to have offered evidence against her husband.

The couple were both registered as profoundly deaf, and have two children aged nine and three.

Paris police headquarters shared a photo this morning of hundreds gathered for a moment of silence in memory of their colleagues who were killed

Iham is now communicating with officers through sign language, making her interview 'very complicated,' said the source.

The victims have been identified as General Damien E., 50, Brice L., 38, Anthony L., also 38, and Aurelia T., 39.

Colleagues described Harpon as a previously trusted employee who had full security clearance to work in the Prefecture's IT department.

The security crisis led to President Emmanuel Macron visiting the building in person, along with his Prime Minister, Edouard Philippe, and Interior Minister Christophe Castaner.

Harpon's ceramic knife would not have activated metal detectors, and he would not have been searched, they head.