Five people have been arrested in the probe into theRadio France and other media reports.
The five were associates of the attacker, Radio France reported, citing a source close to the case.
, which ended when he was shot dead by a sentry in the headquarters courtyard, is provisionally being treated as an act of terrorism.
Five people have been arrested following the killing of four Paris police headquarters staff by a colleague. Source: ABACA
Authorities say the man, a convert to Islam, had contact with suspected members of the ultra-conservative Islamic Salafist movement and had expressed support for the deadly Islamist attack on the satirical magazine Charlie Hebdo to a colleague in 2015.
The attacker's widow was arrested for questioning after the attack but was released without charge three days later.
Police officers patrol outside the police headquarters in Paris, a day after the knife attack. Source: AP
France faced a wave of Islamist attacks, mostly claimed by the Islamic State extremist group, in 2015 and 2016, with more than 230 victims.
There have been several smaller attacks since then.
