I've run police procedural campaigns in Savage Worlds, though that was a cross with urban fantasy and pulps, and in A Dirty World. The former had more action, while the latter featured a private investigator that wasn't a cop, but had a tarot practice.
Let's just say she relied less on tarot and more on talking to people she suspected, though:D!
So I can definitely recommend A Dirty World, and the One-Roll Crime Generator would be useful even if you use a different system!
The Esoterrorists and Mutant City Blues are also focused on police procedurals, it seems the latter would be somewhat better.
I was once upon a time going to write a game around police procedurals - I had a title (Ecce Homicide) and cover already made. I don't give a fuck if my games sell or not, and it looked right up my alley. I have run dozens of police procedurals over the years, with terrific success. But then, while I was prepping the book, I realized there was no game there. Procedurals are all about how you run a game, not what game you run. I shut that sucker down so fast it's still spinning. It's not my business to tell anyone else how to run a game.
Why the hell not? Do you think GMs are born knowing how to run all genres, or do you think that, say, the LotFP DMG is wrong in explaining you how to run a sandbox with dungeons:)?
Make it a "how to run police procedurals" book, instead! But by all means, write it;)!