“Obviously, there were failings,” Christophe Castaner told TF1 television, but he said he would not resign over the matter as some rightwing opponents have said he should.
Speaking separately on French radio on Monday morning Castaner insisted that there was a “disfunction” in the way warnings were made and acted on but that the failure to stop the attacker was not a “state scandal”.
He said the warnings that were made should have triggered a more in depth investigation of the knifeman.
His radicalisation did not trigger warnings at the right level and at the right time, Castaner admitted.
Castaner has come under fire after initially claiming that Mickael Harpon, a 45-year-old computer expert at the Paris police headquarters, had never given the “slightest reason for alarm” ahead of Thursday's attack.
Investigators later revealed that Harpon had in fact been in contact with adherents of Salafism, the ultra-conservative branch of Sunni Islam.
He had defended “atrocities committed in the name of that religion,” anti-terror prosecutor Jean-Francois Ricard said Saturday.
On Sunday, Castaner said Harpon had caused alarm among his colleagues as far back as 2015, when he defended the massacre of 12 people at the Charlie Hebdo newspaper by two brothers vowing allegiance to Al-Qaeda.
But even though a police official charged with investigating suspected radicalisation among the force questioned the colleagues, none of them wanted to file an official complaint.
“Apparently they decided not to make a report,” Castaner said. “The failure occurred at this moment.
“There was nothing in his personnel file that indicated he might be radicalised… If there had been a sign, maybe we could have avoided this,” he said.
In an interview with French radio on Monday Castaner said he wanted any warning about behavioural changes in any individual suspected of being radicalized to automatically trigger a formal investigation.
Castaner will face questioning by parliament's intelligence commission Tuesday over the attack, its president Christian Cambon said Sunday.
“We're going to try to find out what these failings were,” Cambon told AFP.