CHICAGO » FBI Director James B. Comey said today that the additional scrutiny and criticism of police officers that has come in the wake of highly publicized incidents of police brutality may have led to an increase in violent crime in some cities because it has resulted in less aggressive policing.

With his remarks, Comey lent the prestige of the FBI, the nation’s most prominent law enforcement agency, to a theory that is far from settled: that the increased attention on the police has made officers less aggressive and emboldened criminals. But Comey acknowledged that there is so far no data to back up his assertion and that it may be just be one of many factors that are contributing to the rise in crime.

"I don’t know whether that explains it entirely, but I do have a strong sense that some part of the explanation is a chill wind that has blown through American law enforcement over the last year," Comey said in a speech at the University of Chicago Law School.

Comey’s remarks caught officials by surprise at the Justice Department, where his views are not shared at top levels. Holding police accountable for civil rights violations has been a top priority at the department in recent years, and while the department had no immediate comment today, several officials privately fumed at the suggestion that criticizing the police led to violent crime.

Among the nation’s law enforcement officials there is sharp disagreement over whether there is any credence to the so-called Ferguson effect after the protests that erupted in the summer of 2014 in Ferguson, Missouri, over a police shooting.

"Our officers are very, very sensitive to the climate right now," said Sean Whent, the police chief in Oakland, California. "But I haven’t seen any evidence to say our officers aren’t doing their jobs."

But Comey said that he has been told by many police leaders that officers, who normally would have stopped to question suspicious people, are opting to stay in their patrol cars for fear of having their encounters become worldwide video sensations. That hesitancy has decreased the police presence on the streets of the country’s most violent cities, he said.

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