Mr. Green in the third ending. After being the Plucky Comic Relief and a complete coward the entire movie he gets his moment when Wadsworth reveals he's the real blackmailer and Mr. Green, actually an undercover FBI agent, pulls out a gun and shoots him. When the FBI arrives and asks to know who killed him Mr. Green calmly tells them "I did. In the hall. With the revolver. (...) I'm gonna go home and sleep with my wife." Smile and walk away.
You forgot the best part was Mr. Green backing up his repeated claim of not being the culprit by shouting "Told you I didn't do it!" before opening the door and letting the FBI in.
Made even better by the fact that he was the only person in all three endings to NOT commit a murder.