While this is not true, of course, what IS true is that there are never any consequences for those mistakes. The cops lie (or maybe don't even have to lie), the internal "investigation" clears them, and they're free to make more mistakes with guns.
Once in a while we get lucky.
The Sherrif's son was allowed to leave without consequences a couple of years ago after he got caught beating a confession out of an innocent kid one third his size.