According to Showtime's press release, "Lithgow will play Walter Simmons, an unassuming, mild-mannered suburbanite who has been living a dual life as one of America’s most prolific and deadliest serial killers. Dubbed the 'Trinity Killer' because of his proclivity to kill in threes, he relocates to Miami after being tracked by FBI Special Agent Frank Lundy (Keith Carradine). Brought on to assist in the investigation of Miami’s latest serial killer, Dexter Morgan (Michael C. Hall) becomes fascinated with Trinity’s killing methods and his ability to evade capture for almost three decades."
Lithgow will be in it for the long haul! He’ll be featured in all 12 episodes of Season 4, which is scheduled to premiere September 27th on Showtime.