Just watched an episode of a three part film from the UK called "Red Riding Trilogy". Its based on a very dark book series set in Yorkshire in the '70s and '80s during a rash of serial murders. There were four books, but apparently they only had budget enough to make three of them into movies. In any case, they're quite good and feature high production values and a pretty top-notch cast. Aside from the whole mystery about the serial killer (based on a real case), there's a fairly elaborate conspiracy and large cast of characters with dirty little secrets that prove to be their undoing. The cops depicted are some of the most corrupt I've ever seen, and that counts shows like "The Shield" and movies like "L.A. Confidential". Actually, I'd say its fairly close to a British North Country version of an Ellroy novel crossed with "Zodiac" and "The Wire".
Just be prepared for them to be bleak and fairly brutal; I've seen them listed as "horror" movies, and while there's no supernatural chicanery, they don't pull their punches when it comes to dealing with the ugliness of violence.