Narc (2002)

Narcotics Sergeant Nick Tellis, on leave after a trauma, is called back to investigate the murder of fellow undercover operative Michael Calvess, joined by the victim's unpredictable and brutal ex-partner, Henry Oak. Working together in the back alleys of Detroit, Tellis and Oak delve into a dark investigation that leads them to uncover shocking secrets and question the corruption and morality within the department, encountering unorthodox methods and a brutal truth about Calvess's death.