When former Baltimore cop Peter Moskos returned to his old beat during a ride-along, the banter was lighthearted until his partner said, “Body camera on.” The mood darkened. “You instantly thought, ‘God, what might I say?’” says Moskos, now a criminologist at John Jay College of Criminal Justice. About two-thirds of U.S. police departments now film regularly, the Christian Science Monitor reports. The cameras have put a lens on a job that’s already fraught, difficult, and often thankless. Some say it is all for naught. Studies show the body camera revolution hasn’t curbed police shootings of unarmed Americans, nor has it led to more prosecutions of police officers for misconduct. Yet the cameras have had profound and often positive impacts on policing. For officers, they have become important backup in a video era when controversial arrests go viral.

“We have seen how easy it is for people to view or frame facts differently, and we’ve seen how difficult it is to make any progress on any issue where people aren’t working from the same set of facts,” says Christy Lopez, a former Department of Justice civil-rights official. The spike in cameras occurred in 2016, when 25 large cities bought them. At least 16 states have rules for how to maintain citizen privacy with camera footage, and how videos should be released to the press. The expectation among police critics was that widespread adoption of cameras would curb misconduct, lead to more prosecutions of officers on murder charges, and reduce the number of killings. A study by the Washington, D.C., police department in 2017 showed that officers with live body cams used force and faced civilian complaints at about the same rates as officers without cameras. Prosecutions of police officers have remained steady at about 10 per year since 2005 – one officer charged for every 100 deadly shootings.