Regardless, when it happens, it's still a police force, so you still have esprit de corps, "blue wall of silence" and "DA doesn't feel like prosecuting people they work with day to day" effects, and evidence is quite frequently not gathered or "gets lost". So for example if there is excessive use of force at a protest it wouldn't be unusual for those recordings to be misplaced. Bodycams aren't universal yet, but they're always somehow turned off during excessive use of force. The latest example would be a 16yo refugee who was shot dead with an MP5 (i.e. not standard-issue-24/7-belt-carry for police, something you have to get from the car), all officers had bodycams, no recordings. Five officers were charged with various things (up to 2nd degree homicide) because a citizen made an audio recording of the police action (which is a felony btw.), revealing contradictory and false statements.
Additionally, do you have any figures, even very approximate, for what proportion of the time police bodycams are worn and on and what proportion of incidents have said camera turned off? This helps see if there's a real mismatch/incidence of corruption here.
And putting on masks to obscure your face is illegal in protests in Germany.
See https://de.wikipedia.org/wiki/Vermummungsverbot
[0] I mean that in a legal sense, that's how the police works. Whether stopping the protest is morally the right thing to do or not is a different issue that I don't want to address here.
(*) The generalization is okay in this context, because behavior is pretty uniform and larger protests will have riot police pulled from other states anyway.