Let’s be clear about something: cops almost never get suspended, fired, or charged, merely for being violent, abusive, murderous psychos. Cops see each other doing that constantly, and do nothing about it. (On the very rare exceptions, the cop who speaks out against the abuse is the one who gets fired, threatened, harassed, etc.)
They get “punished” if, and only if, a specific example of police abuse is made public, and lots of people are pissed off, then an individual badge-wearing thug might be hung out to dry by his fellow gang members. It’s not because any of them give a shit ab t justice, or the law. It’s because they fear what the people will do if they don’t at least put on a show of punishing the crooked cops who get caught, on video, showing their true, fascist selves.
The only “internal investigations” that police departments ever do is to “investigate” whether letting a gang thug get away with being a violent asshole is going to cause the rest of the gang too much trouble or not, from public backlash (whether verbally or violently). That is their one and only consideration.