The problem right now is that camera footage is handled by the police departments. Any oversight requires the police to operate in good faith. Thinking back to how many news reports I've seen where the footage was "lost" or "the cameras were not switched on" I don't have any trust in that type of system.
Plus, think of the thousands of hours of footage that is regularly collected. Without some incident or reason to inspect the video, most of the incidents would go undetected.
We really need third party monitoring.