Robert Downey Jr. Paul Avery
Jake Gyllenhaal Robert Graysmith
Mark Ruffalo David Toschi
Dermot Mulroney Martin Lee
David Fincher Director
Jimmi Simpson Mike Mageau
Brian Cox Melvin Belli
Chloë Sevigny Melanie
Adam Goldberg Duffy Jennings
Paul Schulze Sandy Panzarella
John Carroll Lynch Arthur Leigh Allen
Elias Koteas Jack Mulanax
Clea DuVall Linda del Buono
Anthony Edwards William Armstrong
Donal Logue Ken Narlow
Zach Grenier Mel Nicolai
James Le Gros George Bawart
James Vanderbilt Screenplay, Producer
Philip Baker Hall Sherwood Morrill
Richmond Arquette Zodiac 1 / Zodiac 2
June Diane Raphael Mrs. Toschi
David Parker Sound Re-Recording Mixer
Candy Clark Carol Fisher
Ren Klyce Supervising Sound Editor, Sound Designer
Ione Skye Kathleen Johns (uncredited)
Matt Winston John Allen
John Getz Templeton Peck
Charles Fleischer Bob Vaughn
Tom Verica Jim Dunbar
John Ennis Terry Pascoe
Mickey Giacomazzi Stunt Coordinator
Angus Wall Editor
Jason Wiles Lab Tech Dagitz
Karina Logue Woman
John Terry Charles Thieriot
Michael Semanick Sound Re-Recording Mixer
Lee Norris Young Mike Mageau
Bob Stephenson Zodiac 3
Christopher John Fields Copy Editor #4
Jeff Daniel Phillips Informant
Judith Drake Florence Douglas
Adam Trese Detective #1
Michael Rose Navy Project Leader
Barry Livingston Copy Editor #3
Charles Schneider Cabbie / Paul Stine
David Lee Smith Father
George Drakoulias Music Supervisor
Thomas Kopache Copy Editor #1
Keith P. Cunningham Art Direction
Bud Davis Patrolman (uncredited)
Mike Medavoy Producer
Richard Hymns Supervising Sound Editor
Joel Bissonnette Inspector Kracke
JD Cullum Director
Harris Savides Director of Photography
Anna Katarina Society Woman
Donald Graham Burt Production Design
John Mahon Riverside Captain
Arnold Messer Producer
Ceán Chaffin Producer
Ciara Hughes Darlene Ferrin
J. Patrick McCormack Police Commissioner
John Lacy Zodiac 4
Randall Poster Music Supervisor
Marty Lodge Pinole Foreman
Victor J. Zolfo Set Decoration
Danielle McKee Prisoner (uncredited)
Callie Thompson Child Witness (uncredited)
Drew Kunin Sound mixer
Shane Woodson Informant
Jonathon Stevens Music Editor
Brett Rickaby Detective Roy