Jake Gyllenhaal

Robert Graysmith

Mark Ruffalo

David Toschi

Anthony Edwards

William Armstrong

Robert Downey Jr.

Paul Avery

Chloë Sevigny

Melanie

Elias Koteas

Jack Mulanax

John Carroll Lynch

Arthur Leigh Allen

Brian Cox

Melvin Belli

Dermot Mulroney

Martin Lee

Charles Fleischer

Bob Vaughn

Zach Grenier

Mel Nicolai

Philip Baker Hall

Sherwood Morrill

James Le Gros

George Bawart

Donal Logue

Ken Narlow

Richmond Arquette

Zodiac 1 / Zodiac 2

Bob Stephenson

Zodiac 3

John Lacy

Zodiac 4

John Getz

Templeton Peck

John Terry

Charles Thieriot

Candy Clark

Carol Fisher

June Diane Raphael

Mrs. Toschi

Ciara Hughes

Darlene Ferrin

Lee Norris

Young Mike Mageau

Pell James

Cecilia Shepard

David Lee Smith

Father

Jason Wiles

Lab Tech Dagitz

Tom Verica

Jim Dunbar

Jimmi Simpson

Mike Mageau

Karina Logue

Woman

Joel Bissonnette

Inspector Kracke

Matt Winston

John Allen

John Ennis

Terry Pascoe

J. Patrick McCormack

Police Commissioner

Adam Goldberg

Duffy Jennings

Clea DuVall

Linda del Buono

Paul Schulze

Sandy Panzarella

Adam Trese

Detective #1

Thomas Kopache

Copy Editor #1

Barry Livingston

Copy Editor #3

Christopher John Fields

Copy Editor #4

Anna Katarina

Society Woman

Jeff Daniel Phillips

Informant

Cassius M. Willis

Uniform Cop

Judith Drake

Florence Douglas

JD Cullum

Director

Michael Rose

Navy Project Leader

Brett Rickaby

Detective Roy

Bill Seward

TV News Anchor

Ione Skye

Kathleen Johns (uncredited)

Brad Carr

Camera Man (uncredited)

Danielle McKee

Prisoner (uncredited)

Bud Davis

Patrolman (uncredited)