(at around 52 mins) One of the books Robert Graysmith has in 1969 has a barcode on the back. Barcodes did not even exist in any stores until the summer of 1974, and most items did not contain barcodes for several years after that.
(at around 55 mins) On the evening of her abduction on March 22nd, 1970, Kathleen Johns is shown driving down Highway 132 while Lynn Anderson's "Rose Garden" is playing on the radio. "Rose Garden" wasn't recorded until September 10th, 1970 and wasn't released as a single until October 8th, 1970.
(at around 1h 9 mins) When Avery is meeting someone in an abandoned building, and in the following scene where Graysmith and his date race to telephone Avery, a traffic signal in the background shows pedestrian control beacons of the "hand/man" style, rather than the "walk/don't walk" style of that era.
(at around 1h 8 mins) Chloë Sevigny's character orders penne ala vodka, but that dish wasn't invented until the mid-70s and wouldn't have made its way to an inexpensive San Francisco restaurant until much later.
(at around 34 mins) Although the choice of a mid-fifties Crown bus was correct for the Napa Valley School District at the time, the bus was showing a California passenger car license plate instead of the correct "Exempt" government plate.
In reference to the Paul Stine murder (October 1969), Graysmith says to Toschi that "Most serial killers are male." The English term and concept of "serial killer" is commonly attributed to former FBI Special agent Robert Ressler in the 1970s.
In the overhead shot of Sacramento, besides the 1988 Hyatt Regency being depicted, there is also the Capitol Park "East End" State Office Complex shown at the bottom of the frame, which wasn't built until 2000.
(at around 34 mins) When Graysmith decides to drive his son to school instead of letting him ride the bus, a 1971 Chrysler Newport can be seen parked at the curb behind the bus. The scene is set on October 1969.
(at around 2h 30 mins) The livery of the United Airlines airplanes shown in the establishing shot of Ontario Airport was incorrect, in the 1991 scene. At that time, United Airlines planes had the first Saul Bass ("rainbow") livery, which was white with orange, red, and blue stripes. The liveries on the planes shown in this shot are the "Mainliner" livery, which the airline had retired, in the mid-1970's, in favor of the Bass design.
(at around 1h 40 mins) When Robert Graysmith visits Paul Avery at his boathouse, you can see "Pong" on Avery's TV. As the scene plays out, you can hear the Pong ball bouncing around for a while, then the sound of the ball scoring. But it's the same shot of the ball bouncing once, then going past the paddle on the right and scoring.
(at around 1h 45 mins) Graysmith says he is an "Eagle Scout, first class." There is no such award as Eagle Scout first class. There is a rank of First Class in Boy Scouting, but it is much lower than Eagle.
(at around 56 mins) When Zodiac is "fixing" Kathleen Johns' wheel, he is seen in the mirror twisting the wheel nuts clockwise, as if to tighten them (which he was supposed to be doing), but if the wheel were to fall off, he should have been twisting anti-clockwise to loosen the lug nuts.
(at around 1h 40 mins) When Robert Graysmith is in Paul Avery's house after he is retired from the Chronicle, the score is 15-9 on the screen displaying Pong. However, another shot is taken and the score is 14-9, but instantly changes back to 15-9.
(at around 2h 20 mins) Robert Graysmith follows Robert Vaughn's car to Vaughn's house in the pouring rain. Vaughn lets Graysmith in his house, offering to hang up Graysmith's wet jacket. Graysmith politely but hurriedly refuses. Next, Graysmith enters the kitchen and sits at the dining table, his back to the camera. His jacket is now dry.
(at around 2h 20 mins) When Graysmith looks at the print out of Allen's driver's license his middle name is spelled "Leigh". But when Graysmith goes to the hardware store to see Allen the name on his shirt is spelled "Lee". (This may have been intentional, as someone preferring the name of Lee would gave been more likely to use the conventional spelling.)
(at around 1h 24 mins) When Inspector Toschi hands Arthur Leigh Allen's watch to Inspector Armstrong, the time jumps ahead about 2 minutes instantly. Also during the hand-off, the bezel rotated about 40 seconds counter-clockwise, as shown by the black indicator marking.
Interior shots of the gold '63 Corvair contain errors. Some are shot in a two-door coupe and others are shot in a four-door sedan model. In one shot, the door-lock button for the rear door can be seen. And the rear-side window profile is distinctly different from one shot to another.
(at around 47 mins) The scene where Melvin Belli is to meet the Zodiac impostor at St. Vincent De Paul's Thrift Store in Daly City is actually filmed on the corner of 26th Ave. and Irving Street in San Francisco's Sunset District. In the background, the Sunset Supermarket can be seen, which did not have Chinese characters displayed at the time the movie took place.
(at around 1h 40 mins) When Robert Graysmith visits Paul Avery at his boathouse, you can see "Pong" on Avery's TV. If Avery had been playing the game in one-player mode, the paddle on the right would have been controlled by the computer, and it would have been moving to block the shot. Moreover, 15 is the game point on "Pong." Once this is reached, the ball disappears until the game is reset. If it is left on for a long enough time, it will go into the Demo mode. But in Demo mode, there is no sound.
(at around 1h 12 mins) Aboard the PSA flight to southern California, the flight attendant makes an announcement over the speaker stating that "smoking is allowed only in the last six aisles." No airplanes have six aisles; presumably she meant to say "the last six rows."
(at around 1h 11 mins) The interior of the PSA flight boarded by the detectives and Paul Avery reveals 5-across coach seating, standard fare for a DC-9, a popular airplane in the 1960s-1970s. The lady seated behind David, however, is holding a safety card reading "727-200," an airplane which seats 6-across in coach.
(at around 24 mins) The taxi driver picks up his murderer on Geary St. in the theatre district. As the camera follows overhead, trolleybus power lines are visible. However, Geary St. did not have trolleybuses, so the power lines are appear in error. The 38 Geary bus route, one of the longest in San Francisco, was always a diesel route.
(at around 6 mins) The movie starts with the July 4, 1969 shootings. Then, the caption on the screen reads "4 weeks later - San Francisco, CA" and we see Robert Graysmith bringing his son to school. Four weeks after July 4 would've been August 1. (Moments later, one of the characters confirms the date as being August 1.) School wouldn't have been in session on August 1. Furthermore, Graysmith, his son, and people on the street are dressed inappropriately for August 1, wearing clothing that would be more suited for late October in New England, not a sunny day in San Francisco in the middle of summer.
(at around 1h 11 mins) The interior of the aircraft depicted for the flight south to check out the Riverside lead shows only 5-abreast seating, which was not what the 727-200 (shown in the establishing shot) had, when PSA flew the type (it was 6 abreast).
(at around 2h 15 mins) When Graysmith arrives home after fleeing the Vaughn house in fright, he fails to turn the wheels of his car toward the curb. This is very important in a hilly place like San Francisco, where they aggressively enforce parking laws, not to mention the safety concerns.
Actors in the film pronounce "Vallejo," the name of the town, the way outsiders tend to - they assume it's "Vuh - lay - ho." Locals, however, which would definitely include police and even San Francisco reporters, pronounce it "Vuh - lay - o."
(at around 24 mins) Graysmith and Arthur Leigh Allen both refer to "The Most Dangerous Game" as a book or a novel. It isn't; it's a short story. However, it is entirely possible that the characters only refer to it as such because are subconsciously simplifying their language in conversation with others.
(at around 2h 30 mins) In the store there is a calendar behind the desk that indicates it is February 1980. However, as Graysmith is entering the store, the caption says it is Dec. 20, 1983. The prominent out-of-date calendar may just be a way of showing that the store that Allen works in is a sleepy place where they've forgotten to change the calendar for four years.
(at around 6 mins) When the movie begins, Robert Graysmith is taking his son to school and tells him he (the son) will be spending the night with his mother and Aaron that night. When he drops his son off, he tells him he (Robert) will be giving him a test that night on what he's learned at school. That night, the son is with his dad, Robert - not with his mother and Aaron.
(at around 24 mins) When the Zodiac hails Paul Stine's cab, an illuminated hair salon sign is visible on the other side of the street. However, the reflections seen on the cab's hood and trunk lid are of the modern-day Starbucks Coffee sign at the filming location which was digitally removed in post.