The following video is Colorado and shows a police officer slamming a suspect (not convicted of anything) into a wall and later delivering several punches while the man is in a jail cell.
Without the bodycam footage this officer would still be doing this.
There is still resistance from police departments to have ever second of every officer’s shift recorded. These people have tremendous power and carry with it tremendous responsibility to act properly. The public pays their salaries and the public needs to be able to review their performance. Cost is often cited as the reason for not equipping every officer with a Bodycam. Even when they are easily available for $300.