Righteous Kill (2008)

Genre: Crime | Drama | Mystery | Thriller
Starring: Robert De Niro, Al Pacino, Curtis 50 Cent Jackson, and Carla Gugino
Tagline: Most people respect the badge. Everybody respects the gun.

Plot: Two veteran New York City detectives work to identify the possible connection between a recent murder and a case they believe they solved years ago; is there a serial killer on the loose, and did they perhaps put the wrong person behind bars?

http://www.imdb.com/title/tt1034331/
http://en.wikipedia.org/wiki/Righteous_Kill