PARIS (REUTERS) - France's anti-terrorism prosecutor said on Saturday (Oct 5) an investigation had detected signs of "latent radicalisation" in an attacker who knifed four co-workers to death at police headquarters in Paris this week.

The assailant, an IT worker at the headquarters, went on a rampage on Thursday, killing three police officers and an administrative worker, and wounding at least one other, before being shot dead by police.

Francois Ricard, the anti-terrorism prosecutor, said his office had taken over the probe because of signs the crime was premeditated and because of the nature of injuries found on at least one of the victims.

The prosecutor also said that the attacker had stated a desire to die.

"The context of latent radicalisation" and messages of exclusively religious character the attacker sent to his wife shortly before the crime were added factors, Ricard told a news conference.

The investigation also revealed contacts between the attacker and several individuals who are likely to belong to an Islamist Salafist movement, Ricard said.

The killer, 45, has been identified by officials only as Mickael H.

'DEADLY JOURNEY'

Officials have not said explicitly there was a terrorism motive behind the attack, but handing a case to anti-terrorism prosecutors usually indicates a terrorism link is the focus of inquiries.

In response, the Prime Minister told weekly newspaper Le Journal du Dimanche he had ordered inspectors to review the procedures in place in the intelligence department of the police headquarters and anti-terror intelligence unit to detect signs of radicalisation among civil servants.

Edouard Philippe also defended his interior minister Christophe Castaner who has come under attack from French opposition parties. The far-right National Rally and the centre-right Les Republicains on Saturday called for parliament to launch an investigation into the minister.

Castaner said last Thursday that the attacker had exhibited no warning signs ahead of the deadly rampage.

"I am confident in Christophe Castaner, who expressed what he knew at the moment when he spoke," Phillipe was quoted as saying on Saturday.

Ricard said that during a "deadly journey" the attacker first stabbed two police officers.

A third police officer was killed in another office and an administrative worker died on the stairs.

The attacker was born on the French island of Martinique and had worked at the police headquarters for several years.

He converted to Islam about 10 years ago, Ricard said.