According to Michael Ausiello, renowned actor John Lithgow has been cast in season 4 of Dexter. The Oscar-nominated star will play Walter Simmons (possible spoiler)... a suburbanite who moonlights as the "Trinity Killer" (so-called because he always kills in threes.) Walter will cross paths with Dexter when he relocates to Miami, and becomes something of a hero to him... (possible spoilers end) In related news, Keith Carradine will reprise his role as Agent Lundy from season 2. Dexter returns 27 Sept on Showtime.