When Martin Sheen's character and his partner go door-to-door interviewing potential witnesses, the second door they knock on is answered by a guy with shaving foam on his face. The guy is 'Charlie Sheen'. He slams the door on the two officers and Martin Sheen quips, "Nice boy."
Real-life Detective Ed Zigo, who appears in the film as a negotiator with a megaphone, was on set during filming as a technical adviser.