FBI Director James Comey reignited the factious debate over a so-called “Ferguson effect” on Wednesday, saying that he believed less aggressive policing was driving an alarming spike in murders in many cities.

Comey said that while he could offer no statistical proof, he believed after speaking with a number of police officials that a “viral video effect” — with officers wary of confronting suspects for fear of ending up on a video — “could well be at the heart” of a spike in violent crime in some cities.

“There’s a perception that police are less likely to do the marginal additional policing that suppresses crime — the getting out of your car at 2 in the morning and saying to a group of guys, ‘Hey, what are you doing here?’” he told reporters.

Comey was wading back into a dispute from last fall that pitted him against some of his bosses at the White House and the Justice Department, the New York Times reports.

He first raised the idea in October that a “chill wind” had deterred aggressive policing. But Obama administration officials distanced themselves from Mr. Comey at the time. They said they had seen no evidence to support the idea of a “Ferguson effect.”