You are right but the police have already figured out that when they want to murder someone they can just turn them off.
That’s partly my point - turning them off would be an admission that the officer intended to do something that he didn’t want anyone else to see.
This is exactly how it should be viewed when they try to disallow people from videoing their actions while on duty.
When taken to court, the officer should be immediately suspected of doing something malfeasant.