"We found essentially that we could not detect any statistically significant effect of the body-worn cameras," says Anita Ravishankar, a researcher with the Metropolitan Police Department and a group in the city government called the Lab @ DC.
Ravishanka's group worked with local police officials to make sure that cameras were handed out in a way that let the researchers carefully compare officers who were randomly assigned to get cameras with those who were not. The study ran from June 2015 to last December and concluded that it didn't make a major difference in police behavior if they had a camera attached or not
It was noted to NPR that a lot of recent footage showing police violence has come from bystander video, not officer body cameras. With everyone having cellphones these days and social media being a part of everyone's daily lives, you see the violence online first and judge it their instead of in full detail.