-
Adam Goldberg as "Duffy Jennings"
-
Adam Trese as "Detective #1"
-
Anthony Edwards as "Inspector William Armstrong"
-
Barry Livingston as "Copy Editor #3"
-
Bob Stephenson as "Zodiac 3"
-
Brian Cox as "Melvin Belli"
-
Candy Clark as "Carol Fisher"
-
Charles Fleischer as "Bob Vaughn"
-
Charles Schneider as "Cabbie/Paul Stine"
-
Chloë Sevigny as "Melanie"
-
Ciara Hughes as "Darlene Ferrin"
-
David Lee Smith as "Father"
-
Dermot Mulroney as "Captain Marty Lee"
-
Doan Ly as "Belli's Housekeeper"
-
Donal Logue as "Captain Ken Narlow"
-
Ed Setrakian as "Al Hyman"
-
Elias Koteas as "Sgt. Jack Mulanax"
-
J. Patrick McCormack as "Police Commissioner"
-
Jake Gyllenhaal as "Robert Graysmith"
-
James Carraway as "Shorty"
-
Jason Wiles as "Lab Tech Dagitz"
-
Jimmi Simpson as "Mike Mageau"
-
Joel Bissonnette as "Inspector Kracke"
-
John Carroll Lynch as "Arthur Leigh Allen"
-
John Ennis as "Terry Pascoe"
-
John Getz as "Templeton Peck"
-
John Hemphill as "Donald Cheney"
-
John Lacy as "Zodiac 4"
-
John Mahon as "Riverside Captain"
-
John Terry as "Charles Thieriot"
-
Jules Bruff as "Catherine Allen"
-
Karina Logue as "Woman"
-
Lee Norris as "Mike Mageau - Young"
-
Mark Ruffalo as "Inspector David Toschi"
-
Matt Winston as "John Allen"
-
Michel Francoeur as "Man on Marquee"
-
Patrick Scott Lewis as "Bryan Hartnell"
-
Paul Schulze as "Sandy Panzarella"
-
Pell James as "Cecilia Shepard"
-
Penny Wallace as "Mulanax's Secretary"
-
Philip Baker Hall as "Sherwood Morrill"
-
Richmond Arquette as "Zodiac 1 & 2"
-
Robert Downey Jr. as "Paul Avery"
-
Thomas Kopache as "Copy Editor #1"
-
Tom Verica as "Jim Dunbar"
-
Zach Grenier as "Mel Nicolai"