There's one case of what you mean that it took me forever to know about.
In PRESCRIPTION: MURDER there's the "Tommy" character, who makes the false confession. He's played by an actor named Anthony James, who's evidently made a career out of playing "spooky" characters. For one thing, he's the comical assassin in NAKED GUN 2 1/2. But maybe his most famous role is the chauffeur in those dream sequences of the movie BURNT OFFERINGS, the one with the dark glasses and the really scary smile.