Haha, oh my god, that's some developement! I'm loving it! Can totally see your poor sim being frustrated with a system that grants immunity to lawbreakers just because they work as cops. And it's intelligence/secret service next for him? Maybe he can bust the corrupt Chief of Police and restore order to the town, after all. Or will he go all villain under the influence of the former co-worker?
One of my cops married the Chief of Police, but she still shows up in her role for my other police sims. Also all playable and townie cops are organized in two clubs. Therefore the Chief is most likely to believe my playable cops when they tell her that a co-worker is the suspect (That's my in-story justification for using the career erasing cheat).