I was actually thinking of it as an extension of the presumption of innocence on behalf of the citizenry and keeping the burden of proof on the government as a check against it's powers. Cops are citizens too but there is some level of surrender of your individual rights e.g., when you join the military. It'd be similar to that.

Another thought is the panopticon: https://en.m.wikipedia.org/wiki/Panopticon . You don't necessarily need to stream and record every cop's cam, just randomize it without indicating to the cops who's getting recorded or when.