FBI Director James Comey cited an alarming spike in murders in many cities, saying he believes it is driven by what he called a “viral video effect,” The New York Times reports. Comey’s comments Wednesday fueled an ongoing debate over what has been called the “Ferguson effect,” in which officers are said to be reluctant to confront suspects because they’re concerned about ending up in online videos.

Comey is quoted telling reporters: “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?’”

Comey noted that he had no statistical evidence, but said that after talking with police officials he came to believe that the effect “could well be at the heart” of increases in violent crime in some cities, The Times reports.

Comey “first raised the idea in October that a ‘chill wind’ had deterred aggressive policing,” the report notes. “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,’ named after the 2014 shooting by a police officer of an unarmed black man in Ferguson, Mo., which sparked widespread protests.”