But this isn't about revenge. It's about rules.
The definitions of non-threat should change for the cop who has been robbed
If you're a cop and you get robbed by a player while you're on duty you are not allowed to kill the player. However, you can go off duty and kill the player to get your money back. So, if you really want to get your money back, just go off duty, kill them and you can get your money back.