Bad Lieutenant (1992)

While investigating a young nun's rape, a corrupt New York City police detective, with a serious drug and gambling addiction, tries to change his ways and find forgiveness. 

Harvey Keitel gives a worryingly convincing performance in the lead role of Abel Ferrara's disturbing drama. Filled with many extreme scenes depicting the cop's escalation into madness and inner turmoil, Bad Lieutenant remains edgy and raw even today as a portrait of a corrupted soul who is struggling to repent, but who can't help but dig himself further into hell.

Not to be confused with the awful 2009 remake featuring the wooden acting of Nicholas cage, this movie is actually about someone who is really walking along the wild side, caught between right and wrong in a crisis of faith.