PARIS — Evidence that the Paris police department missed warning signs about an employee who slashed four colleagues to death at its headquarters on Thursday is prompting demands for a leadership shake-up.

At a news conference on Saturday, France’s antiterrorism prosecutor, Jean-François Ricard, said the killer, a 45-year-old computer technician who worked in police intelligence, had tried to justify to a colleague the killings in January 2015 at the magazine Charlie Hebdo and had done the same for other radical Islamist killings.

[Update: In Paris knife attack, missed signals and calls for vengeance.]

The disturbing statements he made after a dozen people were killed in the Charlie Hebdo attack in Paris were reported to higher-ranking officers, a police union official said Saturday, but nothing was done.

The fact that this and other potential clues — including a video the killer posted on Facebook that imitated throat-cutting — were missed by the police administration that surrounded him, at the heart of an organization dedicated to fighting terrorism, has shocked the ranks of the national police.