Righteous Kill (2008)

A serial murderer walks the streets of Manhattan, targeting violent felons who have fallen through the cracks of the judicial system. All the victims are suspected criminals whose bodies are found accompanied by a four line poem justifying the killing. The killer’s mission is to do what the cops can’t do on their own--take the bad guys off the streets for good. When a notorious pimp becomes one of the killer’s victims, highly decorated detectives Turk and Rooster are called in to investigate. This case could easily be the biggest one in their 30 years on the force. With the unwitting help of a local drug dealer the detectives follow what few clues they have, but their search soon turns inward, eventually leading them full circle as they realize the killer may be one of their own.