In the first movie where Al Pacino and Robert De Niro starred together, The Godfather: Part II (1974), they both played gangsters. In their second movie Heat (1995), Pacino was a cop, and DeNiro was a gangster. In this, their third movie together, they are both cops. This is also the first movie where they have extended interaction. They never shared a scene in The Godfather: Part II (1974) and in Heat (1995) they only had two scenes.
When Robert De Niro, Al Pacino, and Brian Dennehy are speaking about the murder investigation of "Bob Brady", De Niro says, "Seriously, lieutenant, how far do you want us to go with this Rambo murder?". Dennehy was the main antagonist, "Teasle" in Rambo: First Blood.
The initial cut of Righteous Kill ran for two hours, but after a rather negative test screening, Nu Image hastily re-cut the film down to its slender 101 minutes to make it more fast-paced and action-orientated. Snippets of some of the deleted scenes can be seen in the trailer.
The trivia item below may give away important plot points.
Pacino and DeNiro's characters are only ever reffered to by their nicknames Rooster (Pacino) and Turk (DeNiro) through the majority of the film, as to not give away the twist ending that the video "confession" being read by Turk where he reveals that David Fisk aka Rooster is responsible for the ongoing murders that he and Turk are investigating.