[b]Casino[/b] is a great mob movie based on a real guy who at one point was the toast of the town (That town being Vegas!) 

[b]Heat[/b] is widely consider one of the all time great cops and robbers movie with it based on the cat and mouse game of Chicago police officer Chuck Adamson hunting down a criminal named McCauley.

[b]The French Connection[/b] is one of my favorite movies of all time. Based on a real story (All the great ones are!) 

For what you are looking for and for possible ideas I would highly recommend [b]Nightcrawler[/b]. 

To wash this heavy film list down with some light comedy I would circle back to [b]The Nice Guys[/b].

There are other obvious ones like The Godfather, The Departed, and many many more!

I went way too Mafia with this list. For Murder Mysteries there is a fun rule of thumb. You always find out who did it... by the end of the hour. Basically it means tv shows do the murder mystery better than most movies do. Clue, Murder on the Orient Express (70's version) and Knives Out (The recent ray of sunshine of what is an otherwise bleak list).

I would also like to recommend Death in Paradise! It fits the perfect cut on the classic Who Done It mold and with the different lead detectives you get basically all the classic personality and solve types you see in other shows. Murder She Wrote is also a true gold standard and can be a lot of fun if you recall or enjoy seeing random actors from the late 80's and 90's