The Zodiac killer uses, as he tells the police in a phone call, a "Nine millimeter Luger" during his opening shooting of Darlene Ferrin and Mike Mageau in Vallejo on July 4, 1969. Later, Toschi finds a 9 mm Luger casing at the scene of the cab driver's murder. This was the same sort of pistol he had used during the actual killings as well.
During his Lake Berryessa stabbings of Bryan Hartnell and Cecilia Shepard, the Zodiac killer holds a M1911A1 on them. When Bryan asks if the gun was loaded, the Zodiac removes the magazine to show him the .45 rounds inside.
San Francisco Inspector Dave Toschi (Mark Ruffalo) carries a snubnose revolver in his shoulder holster, never drawing it throughout the course of the film.
After the Zodiac killer threatens his life, San Francisco Chronicle journalist Paul Avery (Robert Downey Jr.) asks Toschi for a gun and is subsequently seen firing off rounds from a Colt Official Police at a gun range. In real life, Avery was known to begin carrying a .38 revolver after he was threatened by the Zodiac.
San Francisco Inspector Bill Armstrong (Anthony Edwards) keeps a Smith & Wesson Model 10 in his holster and, like his partner Toschi, never draws it throughout the film.
Armstrong finds a ".22 automatic" inside Arthur Leigh Allen's house. It is described in dialogue as a '22 automatic' and it looks very much like a Ruger Mk I (aka the Standard, since the Mk I target had a longer barrel).
