Common Sense Note
Parents need to know that there is an abundance of obscene language, the F-word most prominent. Violence gets pretty severe too. In a flashback (which may not reflect actual events) children and a mother are murdered by their own husband/father. There is an overwhelming sense of film noir-style corruption, and even the police don't look terribly clean.
Characters tell off-color anecdotes.
Brief, stylized flashbacks of a rape. Characters beaten, shot at close range and in the head. Gasoline poured on an occupied police car, set on fire. A mother and children are murdered in a flashback.
Lots and LOTS of swearing, especially the f-word, plus just about every other profanity from time to time.
Nobody here is very noble, with just a hint that cop-turned-crook Dean Keaton was on the verge of mending his ways for his girlfriend's sake (but didn't). Even the police are portrayed as internally corrupt and bullying, using threats and intimidation on suspects.
Drugs / Tobacco /
Characters smoke -- even through their stocking masks. Mentions of cocaine and other narcotics in terms of underworld drug deals.