Why don't we invent something like that? With hard-set rules, but with enough flexibility so that the game is more fun?
I can imagine a sort of D&D campaign with this.
Great idea. I don't have the time commitment available to produce anything like this, though.
If you go ahead with this plan, can you make its own thread for it? For now, I want to use this thread as a place to leave RPGs I find on the theme, as well as to continue getting suggestions.
So far, I've found
Leverage, apparently based on some TV show. Will give the previews a look, though the Cortex systems never get any support. Also, this seems more 'Super Spy' than 'Street Criminal'.
There are 38 core rulebooks in the 'Modern, Detective/Crime' genre. Most are not quite what I'm looking for, either (with bits like time travel superhereos tossed in).
Mean Streets looks like a mid-20th century take on the concept.
Dogtown, is a game which is now free (though you have to log-in. It looks to be a part of RPGnow, so I will check to see if my RPGDriveThru account will work), that seems to be set in the 70s.
Found a sourcebook called 'Mobsters' using something called the 'Scorpio system'. Unfortunately, the only place I can find info on either of these things is inside somebody's massive collection of pirated RPGs, so there's no link. It seems to me like enough of an indication that's it's probably not the best choice anyway.
There are multiple sourcebooks for the mafia in d20 Modern, but that goes without saying.