PARIS (AP) — France's interior minister on Tuesday posthumously bestowed France's highest award, the Legion of Honor, on the four victims of last week's knife attack at the Paris police headquarters.

Christophe Castaner honored the victims during a morning ceremony at the site of the killings in which a longtime police employee stabbed four colleagues to death before being shot dead by police.

French prosecutors are investigating the killings as a potential act of terrorism.

The ceremony came as justice officials said French investigators found a USB stick belonging to the killer, a technology administrator in the police intelligence unit, containing information about his colleagues.

But officials did not immediately confirm several French media reports that the memory stick contained "jihadi propaganda."

Castaner has acknowledged breaches in security over a failure to detect signs of the radicalization of the knifeman, a police employee.

French President Emmanuel Macron led a national tribute to the slain employees with a speech at the police headquarters following the event. He is also meeting privately with the families of the victims.