The Zodiac Killer is an unidentified American serial killer who is believed to have murdered at least five people in Northern California between 1968 and 1969. An earlier murder involved the stabbing death of an 18-year-old college student in Riverside, California in 1966, who is speculated to be attributed to the Zodiac Killer. This case inspired the influential 1971 action film “Dirty Harry,” which starred Clint Eastwood. This later became the subject of the critically acclaimed David Fincher dramatic film “Zodiac” in 2007.

In 1968, a teenage couple was shot to death near their car in a remote area north of San Francisco. One year later, another couple was attacked in similar circumstances; however, the male victim survived. After the 1969 attack, the killer phoned police to alert them of the crime and to take responsibility for the 1968 murders. Later that year, the Zodiac Killer attacked another young couple, though once again, the male appeared to have survived. The last known victim was a taxi driver, who was shot in October of 1969.

The murders were the subject of intense investigation and media coverage, particularly because of the killers’ taunting letters to newspapers and phone calls to police. His letters, sent from 1969 to 1974, were signed with a symbol resembling the crosshairs of a gunsight and typically began with the phrase “This is the Zodiac speaking.” Included among the letters were four ciphers or cryptograms; the first was sent in three parts, which would then be sent to three separate Bay Area newspapers in July of 1969. Known as the “408 ciphers” for the number of characters they contained, the letters were soon decimated by a pair of private citizens.

The message stated, “I like killing people because it is so much fun.” Another cipher, the “340 ciphers,” was mailed to the San Francisco Chronicle in November 1969. This cipher was finally decimated in 2020 by a team of three amateur code breakers. Its message began, “I hope you are having lots of fun trying to catch me.”

Lots of things about this case remain mysterious when it comes to the Zodiac Killer. One of these is the issue of when the crimes stopped. Crime writer Robert Graysmith argued that the Zodiac Killer remained active throughout the 1980s. After several investigations, investigators claimed to have identified the zodiac killer. The suspect was Arthur Leigh Allen, a school teacher from Vallejo, California, who had been institutionalized in 1975 for child molestation, though his identification with the Zodiac Killer has never been confirmed.