Numerous letters of contested or unconfirmed authorship were attributed to the Zodiac Killer over the years:
- A February 14, 1974 letter to the San Francisco Chronicle claimed the Symbionese Liberation Army’s initials spelled an Old Norse word meaning “kill”; the handwriting was not authenticated as Zodiac’s.
- A May 8, 1974 letter signed “A citizen” criticized the film Badlands as “murder-glorification”; its tone and sarcasm resembled Zodiac’s.
- A July 8, 1974 anonymous letter complaining about columnist Marco Spinelli was signed “the Red Phantom (red with rage).”
- A May 6, 1986 letter claimed 100+ killings across California and Nevada.
- An October 27, 1987 letter to the Vallejo Times-Herald threatened to drive around on Halloween “looking for some kiddies to run over.” The authorship of the 1986 and 1987 letters is debated.
See also the Albany Times Union letter (1973) and the 1990 Eureka Christmas card.