Jake Gyllenhaal Robert Graysmith
Robert Downey Jr. Paul Avery
Dermot Mulroney Martin Lee
Mark Ruffalo David Toschi
Brian Cox Melvin Belli
Chloë Sevigny Melanie
Jimmi Simpson Mike Mageau
Elias Koteas Jack Mulanax
David Fincher Director
Anthony Edwards William Armstrong
Clea DuVall Linda del Buono
Stanley B. Herman Staff Editor
Adam Goldberg Duffy Jennings
John Carroll Lynch Arthur Leigh Allen
Donal Logue Ken Narlow
Ione Skye Kathleen Johns (uncredited)
Paul Schulze Sandy Panzarella
Karina Logue Woman
June Diane Raphael Mrs. Toschi
Barry Livingston Copy Editor #3
Zach Grenier Mel Nicolai
Candy Clark Carol Fisher
Jason Wiles Lab Tech Dagitz
Thomas Kopache Copy Editor #1
Charles Fleischer Bob Vaughn
John Getz Templeton Peck
Tom Verica Jim Dunbar
Matt Winston John Allen
Philip Baker Hall Sherwood Morrill
John Lacy Zodiac 4
George Drakoulias Music Supervisor
James Vanderbilt Producer, Screenplay
John Ennis Terry Pascoe
Lee Norris Young Mike Mageau
Adam Trese Detective #1
David Lee Smith Father
James Le Gros George Bawart
Bob Stephenson Zodiac 3
Jeff Daniel Phillips Informant
Drew Kunin Sound mixer
Michael Rose Navy Project Leader
Joel Bissonnette Inspector Kracke
Richmond Arquette Zodiac 1 / Zodiac 2
John Terry Charles Thieriot
Pell James Cecilia Shepard
Mickey Giacomazzi Stunt Coordinator
Judith Drake Florence Douglas
Brett Rickaby Detective Roy
Christopher John Fields Copy Editor #4
John Mahon Riverside Captain
Ciara Hughes Darlene Ferrin
Jules Bruff Catherine Allen
Callie Thompson Child Witness (uncredited)
J. Patrick McCormack Police Commissioner
JD Cullum Director
Addison Teague Sound Effects Editor
Anna Katarina Society Woman
Keith P. Cunningham Art Direction
Cazimir Milostan Internal Affairs Agent #2
James Joseph O'Neil DOD Project Leader
Mike Medavoy Producer
Betty Murphy Informant
Richard Hymns Supervising Sound Editor
Cassius M. Willis Uniform Cop
Daniel M. Stillman Unit Production Manager
Merrick Morton Still Photographer
Bud Davis Patrolman (uncredited)
John Hemphill Donald Cheney
Ted Garcia Anchorman #1
Ceán Chaffin Producer
Danielle McKee Prisoner (uncredited)
Steve Hart Stunts