Comment by tombert

I feel like that is exactly what happens for anything but the most serious crimes. Keep in mind, a lot of internal investigations are not reported to the public and we never hear about them. Part of the reason that they're "internal" is so that they stay internal; we only hear about ones that leak.

Even for very serious crimes (e.g. sexual harassment or assault) these internal investigations end up being "sufficient", and the police don't bother.