Narc (2002)

Tells the dark story of suspended undercover narcotics officer, Nick Tellis (Jason Patric), who is reluctantly drawn back onto the force to find the truth behind the murder of a young police officer killed in the line of duty. He is teamed with Henry Oak (Ray Liotta), the slain officer's partner, a rogue cop who will stop at nothing to avenge his friend's death. As Tellis and Oak unravel the case, the dark underbelly of the narcotics world reveals itself in surprising ways.