The Zodiac's first confirmed attack - the murders on Lake Herman Road - was excluded from the film, since there were no surviving victims to corroborate details. The creators thus decided to open the film with the 4th of July murders, considered to be the Zodiac's second double murders.
(At around 1 hour 40 minutes) The real-life Zodiac survivor, Bryan C. Hartnell, makes a cameo with his wife in the police station when Dermot Mulroney's character asks Mark Ruffalo's character if he wants a hug on the stairs. Bryan and his wife walk by in the background.
David Fincher, screenwriter James Vanderbilt, and producer Bradley J. Fischer spent 18 months conducting research into the Zodiac murders. They interviewed witnesses, family members, suspects, retired and active investigators, the only two surviving victims, and the mayors of San Francisco and Vallejo.
(At around one hour and thirty-five minutes) Scenes of Dave Toschi and Robert Graysmith watching Dirty Harry (1971) were filmed inside the Mann National Theatre in Westwood, California. The garish color schemes of the movie theater were not added by the art department. The very retro interiors of the theater had remained unchanged since 1969, when the National was first built. Interestingly, this film played at the Mann National Theatre in mid March of 2007. Thus, actual moviegoers watched celluloid moviegoers occupying their seats, on the National's trademark large screen. The theater has since been torn down.
Anthony Edwards was cast as Armstrong because David Fincher wanted him to be played by a thoroughly decent person. Fincher already knew him, not so much from his work on ER (1994), but because he was a neighbor.
Robert Downey Jr. was so unaccustomed to the experience of both David Fincher's multiple takes, and the process of filming digitally, that he rebelled against David for "having no time to get my shit together in my trailer" by hiding mason jars full of his urine on set.
The cab scene on Washington and Cherry Streets in San Francisco could not be entirely shot in San Francisco due to filming restrictions and the opposition of the neighborhood residents. So the production constructed a set replicating the intersection, including the street, apartments, and crime scene at Downey Studios, just outside of Los Angeles. Backdrops of San Francisco were digitally inserted to complete the scene. Only a few seconds of actual footage shot in the original crime scene location remains in the film.
South Korean film director Joon-ho Bong has classified David Fincher's film as a "masterpiece," writing that "There was really nothing to find fault with about it, down to the cinematography, art direction, and action."
As Robert Graysmith drives his son to school, the broadcaster on his car radio makes a reference to the then-forthcoming free concert by The Rolling Stones at the Altamont Speedway. It was Melvin Belli's recommendation to the Rolling Stones to hold this particular concert.
This film pays homage to Dirty Harry (1971), whose foe, Scorpio, was based on the Zodiac murderer. Another fictional policeman also encountered a foe called Scorpio around this time. In the Robert Graysmith book, they note that around the time of the Zodiac murders, the police investigated a possible connection to the Dick Tracy comic strip, as Dick Tracy faced a Zodiac-themed gang directed by a mastermind called Scorpio.
Shane Salerno optioned the Robert Graysmith book "Zodiac" when he was just nineteen years old, and developed it with Graysmith for several years, before selling it to Disney's Touchstone Pictures in a seven-figure deal. Salerno wrote several drafts of the screenplay before multiple administration changes at Touchstone derailed the project.
Paul Avery did not withdraw from working at the San Francisco Chronicle to a life of reclusive obscurity as the film suggests. In the mid-1970s, he reported on the kidnapping of Patricia Hearst and turned his reports into a book: "The Voices of Guns" (1976). He was also married with two daughters, a fact not mentioned in the film.
George Lucas gave an interview to Empire magazine once stating that the Zodiac murders captured his imagination at the time as a high schooler and then college student at USC, and he always felt like Toschi was harshly judged for how the investigation was handled. He explained this is why he named a location on Tatooine Tosche Station, in honor of the SFPD inspector.
Variety reported on July 6, 2005, that Gary Oldman had signed to portray attorney Melvin Belli in this film, and a later story in the Hollywood Reporter stated that he had done so. On February 14, 2006, Gary Oldman's management company, The Douglas Management Group, issued a statement that the Hollywood Reporter story was not true, and that "Mr. Oldman is not in the film, and never was." However, in an interview on March 2, 2007, with Cinematical, the "Zodiac" author Robert Graysmith stated, "Now we had Gary Oldman at one point, to play Melvin Belli. He went to a lot of trouble, they had appliances, but just physically it wasn't going to work, he just didn't have the girth."
In multiple scenes throughout the film's soundtrack, a lone trumpet is frequently heard playing a four-note motif, and is an homage to a piece by American composer Charles Ives, aptly entitled "The Unanswered Question".
(At around forty-four minutes) Television host Jim Dunbar mentions Melvin Belli's appearance on Star Trek (1966) in the A.M. San Francisco scene. Belli guest-starred in Star Trek: And the Children Shall Lead (1968), which first aired on October 11, 1968.
The U.S. Blu-ray released by Paramount Home Video had a very limited run. For a while, the Blu-ray became one of the rarest on the market; fetching prices close to one hundred dollars from second-hand online retailers, until Warner Home Video acquired the Paramount catalogue in 2012, and re-released it the following year.
(At around one hour and forty-five minutes) In the restaurant scene, where Robert Graysmith is treating David Toschi to a hamburger, Toschi chews the hamburger for some time before spitting the chewed food into a napkin. The reason for this was because Mark Ruffalo, who played Toschi, is a vegetarian and refuses to consume meat. (One hour and twenty minutes into the movie, Toschi cadges half of his partner's BLT and then removes the bacon from it before eating it.)
After Zodiac's bus threat is released to the public, Robert is discussing "The Water Theory" in regards to how Zodiac chooses his victims (Lake Berryessa, Blue Rock Springs, Washington and Cherry.) The film's palette makes the color blue very prevalent in most of the scenes. Some examples include: Zodiac's letters are written in blue ink. The first is read by the Editor, who is wearing a blue shirt. When reading the decoded cipher, thus introducing Avery and Graysmith to each other, they are both wearing blue shirts. Robert is wearing a blue shirt in every scene he's in. In Morti's, Graysmith introduces to Paul Avery a blue drink called an Aqua Velva. In the following shot, with the multiple empty glasses, the song "Crystal Blue Persuasion" by Tommy James & The Shondells plays. Melvin Belli's suit is navy blue, with a light blue shirt. The woman who pulls over to help a Zodiac victim, is wearing a blue jacket. Dave Toschi's suit is light blue when reading Zodiac's Halloween card. Paul Avery's shirt on the airplane is blue. Arthur Leigh Allen's work coveralls are dark blue. When Robert is on the phone, while his kids are going over his files, the shirt he wears, and the phone are blue.
Although Toschi and Armstrong are San Francisco Police Department Inspectors, their actual responsibilities are identical to those of detectives in other municipal police organizations. The San Francisco Police Department calls their detectives "inspectors". (Which anyone who has ever seen a police drama set in San Francisco knows.)
(At around twenty-four minutes) The phone number 626-2345 displayed on the Yellow Cab in the film, was the actual phone number for the Yellow Cab Company in San Francisco. By the time that the film was released, the number had been changed.
The Warner Brothers and Paramount logos used at the start of the film are almost identical to the ones used by the respective studios in 1969, but not completely. In the case of Warner Brothers, their 1969 releases did not use their classic shield as depicted here, but instead carried a "Warner Bros.-Seven Arts" logo, used when the studio had merged with Ray Stark and Eliot Hyman's production company, Seven Arts. As for the Paramount logo, where it would have read "A Gulf+Western company" in 1969, it now reads "A Viacom Company", reflecting current ownership.
In the flyover shot of the early construction of the Transamerica Pyramid, the "box" foundation is completely devoid of any piles or columns. Unlike most conventional high-rise foundations, the Pyramid was uniquely constructed without any piles driven into the bedrock. The weight of the building actually rests on trusses at the first two levels, and the trusses rest on top of this "box".
Though Callahan's Diner was a set built for the film, the Callahan's Diner logo and window script is identical to that used by Callahan's Diner at 1213 Wilshire Boulevard in Santa Monica, California. It's quite likely that members of the cast and/or crew of the film were familiar with the Santa Monica restaurant and used it as an art model for the San Francisco locale. The "Dirty Harry" reference inherent in the diner's name may simply be an added plus.
Toschi flies to Riverside on PSA (Pacific Southwest Airlines). PSA was one of the first large discount airlines, operating from 1949 to 1988 when it was integrated into USAir. It is not related to Southwest Airlines.
(At around one hour and thirty-five minutes) Captain Lee tells Toschi to take some time off and "go to Candlestick". Candlestick Park was the home of the San Francisco Giants from its construction in 1960 to 2000, the San Francisco 49ers from 1971 to 2013, and the Oakland Raiders in 1961. In 2014, the 49ers moved to their new home at Levi's Stadium in Santa Clara and Candlestick Park was demolished in 2015.
Mark Ruffalo's character, Dave Toschi, eats animal crackers throughout the film. Ruffalo is a vegetarian in real life (during the diner scene, he's actually seen spitting out a bite of his burger into a napkin because he refused to swallow it). As such, these crackers are the only "animals" Ruffalo actually eats.
Two of the lead actors, Mark Ruffalo and Robert Downey, Jr., would go on to co-star in the Marvel Cinematic Universe as The Hulk and Iron Man respectively. Jake Gyllenhall would also star in Spider-Man: Far From Home (2019), set in the same universe.
In the real investigation, on October 6, 1969, Arthur Leigh Allen was interviewed by detective John Lynch of the Vallejo Police Department. In the movie, Arthur Leigh Allen is played by John Carroll Lynch.
In the film when the suspected killer, Arthur Leigh Allen, is brought in for questioning, a title appears on screen: SEPT. 14, 1972. After he is released on lack of evidence, Inspector David Toschi attends a SPECIAL SCREENING - SFPD on a marquee of the NORTH POINT THEATER which is a screening of DIRTY HARRY. DIRTY HARRY was released on Dec. 22, 1971. In reality, a gala world premiere benefit performance was held for the San Francisco Police Activities League, most likely a few days before the Dec. 22 opening.
In the lobby where the screening of Dirty Harry (1971) is taking place, is a full length standee of Clint Eastwood. While Eastwood's stance is exactly the same as the original 1971 standee for the film, in this version he is pointing his famous .44 Magnum downwards whereas in the original he is pointing the pistol outwards at a horizontal level.
The trivia items below may give away important plot points.
In one of the Zodiac's letters, he muses on who would portray him in a film about him. In this film, he is portrayed by three separate actors, and in any shot featuring the Zodiac, the actor's faces are always out of focus or obscured. This served to keep the audience guessing, and perhaps as a balk to the actual Zodiac killer, so that he wouldn't be portrayed by a visible, or famous actor.
Talks with Sony fell through when the studio insisted that the film should not be any longer than two hours and fifteen minutes. Warner Brothers and Paramount agreed to share the production costs, even though a "talky" film with an inconclusive ending was a tough sell.