Michael Ausiello
May 27, 2009 AT 09:51 PM EDT

Dexter has found its next Big Bad.

Sources confirm to me exclusively that John Lithgow is joining the season 4 cast as Walter Simmons, an unassuming suburbanite who has been living a dual

life as one of America’s most prolific and deadliest serial killers. When the mad man (who is dubbed the “Trinity Killer” because he always kills in threes) relocates to Miami, Dexter becomes obsessed (or inspired?) by his efficient killing methods and ability to evade capture for almost three decades. (This is the new antagonist role exec producer Sara Colleton teased back in April.)

Dexter‘s fourth season premieres on Sept. 27. Oh, almost forgot, bonus casting scoop: Keith Carradine is reprising his role as Deb’s daddy-figure ex, F.B.I. Special Agent Frank Lundy, for multiple episodes.

More Dexter
Ken Tucker applauds Lithgow casting

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