PARIS, Oct. 14 (Xinhua) -- French police on early Monday detained five people related to the man who carried out a deadly knife attack in the Paris police headquarters earlier this month, local media reported.

The five people were arrested in Val d'Oise department in north Paris, and they are believed to have ties with the attacker, state-run France info radio reported, citing a source close to the investigation.

On Oct. 3, Mickael Harpon, a 45-year-old IT assistant expert in the intelligence service, stabbed to death three police officers and one female administrative employee inside the building before he was shot dead by another officer.

Investigators revealed that Harpon had been radicalized and defended "atrocities committed in the name of that religion" related to the Islamist attack on the satirical weekly Charlie Hebdo in 2015, in which 12 people were killed, according to anti-terror prosecutor Jean-Francois Ricard.

They also found a USB key containing details on many of his colleagues and several propaganda videos from the Islamic State group.

French police have often been the target of Jihadist group attacks in recent years due to the country's military intervention in Iraq, Syria and the Sahel region.