Well, at least make cops actually have to go through the trouble to arrest people.
For instance, the cops have three police items: Taser, Stun Baton and Handcuffs. First they incapacitate their target, then put on handcuffs and then pull them over to the police station where they decide what to do with him: transfer him to prison, start a court case or let him go.
And if cops simply murder their target? Well, it ain't gonna pretty for him.
Murder should be one of the capital crimes which gives you a high sentence, and if it's became Flash Mob that guy's probably going to get some electric chair that force-resets his character.
I always wanted to see a Judicial System done in heavy RP gamemodes, though. It's been done in Space Station 13, and, even though it can be a clusterforget, sometimes you can turn an entire case around and find out something bigger than just breaking and entry.
It just needs a little bit of roleplay and discipline, and if the mayor haven't been picking handicaps for the government crew, I think the Judicial system might actually work.
And I think just the Judge should decide the sentence he's going to give. If he's unjust he's going to be fired anyway.