USA Today quotes the head of the Fraternal Order of Police:
The proliferation of cheap video equipment is presenting a whole new dynamic for law enforcement. It has had a chilling effect on some officers who are now afraid to act for fear of retribution by video. This has become a serious safety issue. I’m afraid something terrible will happen.
Over the last year I’ve received email and heard from a number of police officers on radio call-in shows who’ve said that citizen-shot video vindicated them in cases where they had been accused of misconduct. If video has been edited or manipulated, that’s pretty easy to discern should it become a key piece of evidence against a police officer.
We want cops second-guessing decisions that are second-guessable. If an abundance of video cameras helps that to happen, all the better.
But there’s no reason citizen video should make a good cop think twice before using appropriate force to apprehend someone who presents a threat to others. As noted above, he should welcome it, in case the suspect later claims the force was unwarranted.
Ideally police would be recorded all the time. And they'd prefer it that way.