Hmm.
I think you should be looking to take inspiration from your favourite hardboiled crime media, whether books, movies or TV.
Off the top of my head, the following come to mind:
* The Sopranos
* The Wire
* The Shield
* Any amount of Quentin Tarantino movies but especially Pulp Fiction and Reservoir Dogs.
* Classic noir fiction by Raymond Chandler and Dashiel Hammett
* Some personal favourites of mine include Smokin' Aces, and Shoot Em' Up.