Zodiac : Plot

The film begins in July 1969 with the Zodiac killer’s second attack, the shooting of Darlene Ferrin and Mike Mageau at a lover’s lane in Vallejo. Mageau survives while Ferrin dies from her injuries. A letter written by the Zodiac arrives at the San Francisco Chronicle in August of the same year. Paul Avery (Robert Downey Jr.) is the top crime beat reporter covering the Zodiac murders for the San Francisco Chronicle. Robert Graysmith (Jake Gyllenhaal) is a political cartoonist for the same newspaper who receives encrypted letters that the killer sends to the police and several newspapers, taunting them. Because of Graysmith's inexperience and lowly status at the paper, he is not taken seriously by Avery and the editors and is excluded from the initial details about the killings despite his interest in the case. In particular, he is drawn to the encrypted code that is included with the letters and is given access to one. When he is able to crack one of the codes, Avery begins sharing information with him.

The Zodiac killer stabs Bryan Hartnell and Cecelia Shepard at Lake Berryessa in Napa County. Shepard dies as a result of the attack. Soon afterwards, cab driver Paul Stine is shot and killed by the killer in Presidio Heights. San Francisco police detectives Dave Toschi (Mark Ruffalo) and his partner Bill Armstrong (Anthony Edwards) are assigned to the case, liaising with other detectives such as Jack Mulanax (Elias Koteas) in Vallejo, Ken Narlow (Donal Logue) in Napa. The killer, or someone posing as him, continues to toy with authorities by speaking on the phone with celebrity lawyer Melvin Belli (Brian Cox) when he makes an appearance on a television talk show. Meanwhile, Avery and Graysmith become friends, delving deeper into the case.

In 1971, Toschi, Armstrong and Mulanax question Arthur Leigh Allen (John Carroll Lynch), a potential suspect in the case. However, a handwriting expert (Philip Baker Hall) says that Allen did not write the Zodiac letters. Avery receives a letter, possibly from the Zodiac killer, threatening his life. He becomes increasingly paranoid and takes drugs and alcohol to control these feelings. At one point, he shares information with a rival police force which angers Toschi and Armstrong. Avery leaves the Chronicle. Over the course of the decade, Armstrong quits the homicide division, Toschi is demoted for supposedly forging a Zodiac letter, and Graysmith continues his own in-depth investigation, interviewing witnesses and police detectives involved in the case. Due to his obsession for the case, he loses his job and his wife (Chloë Sevigny) leaves him, taking their children with her. Graysmith persistently contacts Toschi about the Zodiac murders and eventually impresses the veteran detective about his knowledge of the case and his theory of the identity of the killer. While Toschi cannot directly give Graysmith access to the information he discovered over the years, he provides contacts of other police departments in counties where the other murders occur and the cartoonist acquires more information that points to Allen as the Zodiac.

In 1983, Graysmith finds Allen at a Vallejo hardware store but does not confront him. In 1991, Mageau identifies Allen from a police mugshot. The film offers much circumstantial evidence which could support that conclusion, while offering possible reasons to doubt the evidence (fingerprints, handwriting, DNA) which legally exonerated Allen. An end title credit states that Allen died in 1992 without ever being charged.