France's interior minister rejected opposition calls for his resignation on Sunday but acknowledged opportunities had been missed to prevent the killing of four police personnel by a radicalised colleague.
"Obviously there were failings, because three men and a woman have been killed," the minister, Christophe Castaner, told TF1 television of a rampage by a man armed with a knife at the main Paris police headquarters on Thursday.
Mickael H, a 45-year-old IT specialist with security clearance, killed three officers and one civilian employee before he was shot dead by another officer.
Earlier signs of the Muslim convert's support for violent extremism have come to light.
Colleagues had flagged comments he made in 2015 celebrating the Islamist attack on satirical weekly Charlie Hebdo, in which 12 people were killed, but no action was taken.
A senior officer had interviewed the colleagues in July 2015 and asked them "whether they wanted to file an administrative report", Castaner said on Sunday. "But they decided not to."
He added: "If at that time there had been a deeper and more effective investigation, I believe we could have avoided this situation."
Castaner was appointed last year to the government of President Emmanuel Macron, who succeeded President Francois Hollande in 2017.
Some opposition politicians have accused the government of playing down the missed clues in the immediate aftermath of the killings and said Castaner should resign.
"The question does not even arise," Castaner said. From the start, he said, "we made it clear we weren't ruling anything out ... And there was no suggestion of radicalisation in this individual's administrative file - unfortunately."
