they are either fired or resign and then go off to some other town and continue to wreak havoc at the new place. That's what happened with the cop who killed young Tamir Rice. He had been on the force at a nearby department and was deemed "unfit", resigned, joined Cleveland's PD (where their HR never bothered to verify his previous record)... and then when he was fired from there after the shooting, he was then accepted at yet another PD until the uproar was so great that he withdrew from the position.