Jake Gyllenhaal

as Robert Graysmith

Born 12/19/1980, age

Mark Ruffalo

as David Toschi

Born 11/22/1967, age

Anthony Edwards

as William Armstrong

Born 07/19/1962, age

Robert Downey Jr.

as Paul Avery

Born 04/04/1965, age

Chloë Sevigny

as Melanie

Born 11/18/1974, age

Elias Koteas

as Jack Mulanax

Born 03/11/1961, age

John Carroll Lynch

as Arthur Leigh Allen

Born 08/01/1963, age

Brian Cox

as Melvin Belli

Born 06/01/1946, age

Dermot Mulroney

as Martin Lee

Born 10/31/1963, age

Charles Fleischer

as Bob Vaughn

Born 08/27/1950, age

Zach Grenier

as Mel Nicolai

Born 02/12/1954, age

Philip Baker Hall

as Sherwood Morrill

Born 09/10/1931

Died 06/12/2022, age

James Le Gros

as George Bawart

Born 04/27/1962, age

Donal Logue

as Ken Narlow

Born 02/27/1966, age

Richmond Arquette

as Zodiac 1 / Zodiac 2

Born 08/21/1963, age

Bob Stephenson

as Zodiac 3

Born 05/18/1967, age

John Getz

as Templeton Peck

Born 10/15/1946, age

John Terry

as Charles Thieriot

Born 01/25/1950, age

Candy Clark

as Carol Fisher

Born 06/20/1947, age

Lee Norris

as Young Mike Mageau

Born 09/25/1981, age

Pell James

as Cecilia Shepard

Born 04/30/1977, age

Jimmi Simpson

as Mike Mageau

Born 11/21/1975, age

Adam Goldberg

as Duffy Jennings

Born 10/25/1970, age

Clea DuVall

as Linda del Buono

Born 09/25/1977, age

Adam Trese

as Detective #1

Born 01/04/1969, age

Thomas Kopache

as Copy Editor #1

Born 10/17/1945, age

Barry Livingston

as Copy Editor #3

Born 12/17/1953, age

Jeff Daniel Phillips

as Informant

Born 07/03/1968, age

Ione Skye

as Kathleen Johns (uncredited)

Born 09/04/1970, age