French police have arrested five people linked to a knifeman who killed four colleagues at the Paris police headquarters earlier this month, reports and sources say.
The arrests took place early on Monday in the northern Paris suburbs.
On 3 October, police IT worker Mickaël Harpon killed three officers and an employee before he was shot dead.
The attack has raised questions about how police failed to notice signs of his radicalisation in recent years.
One of the people arrested is an imam who officiated at a mosque in the town of Gonesse which Harpon attended, reports say.
That imam is on France's "Fiche S" list of potential security risks, one source told AFP news agency; he was not the principal imam at the mosque and did not preach on Fridays, Le Figaro reports.
On Friday, the mayor of Gonesse announced that the Muslim association which employed the imam had dismissed him.
Harpon, who was born on the French island of Martinique, had worked at the police headquarters for several years as an IT expert, and converted to Islam about 10 years ago.
Investigators have said he had been in contact with supporters of Salafism, the ultra-conservative branch of Sunni Islam.
On 3 October, Harpon stabbed three people inside two offices and two women on a stairway of the Paris police headquarters, before he was shot dead inside the building's courtyard.
Three men and one woman were killed. A fifth person was seriously injured. Harpon slit the throat of one of the victims.