From what a policeman friend of mine told me, the busts they spend all their time on have the reverse of that story: a local gang/mob forms, and then, since they're already assaulting and murdering to keep their place in the criminal underbelly of the city, and since they know their shit well enough to be getting away with it, they can run as many side-businesses as they like doing other, lesser illegal deeds, because they've already ensured their protection. This is pride before a fall, because these lesser crimes—especially if they involve non-group others, like prostitutes or drug mules—can be the cracks in the dam that allow the police to nab them.