The series of murders attributed to the Zodiac Killer began on December 20, 1968, in Benicia, northern California, with the deaths of two high school students, Betty Lou Jensen, 16, and David Faraday, 17. The victims were shot while parked near a local beauty spot known as Lovers’ Lane. In letters sent to newspapers, the assailant claimed to have used a .22-caliber semi-automatic handgun in the attack.

The killer struck again on July 5, 1969, targeting Darlene Ferrin, 22, and Mike Mageau, 19, at Blue Rock Springs Park in Vallejo, another locale favored by courting couples. Ferrin was killed, but Mageau survived despite being shot four times. Mageau told authorities that the assailant opened fire silently.

On September 27, 1969, the Zodiac attacked a third couple, Bryan Hartnell, 20, and Cecelia Shepard, 22, while they were picnicking at Lake Berryessa in Napa County. The attacker tied up and stabbed the pair, wearing a hood resembling an executioner’s mask adorned with a crosshair symbol on the chest. Shepard died, but Hartnell survived. The killer left the crosshair symbol and a list of prior attack dates on Hartnell’s car door, which would become a distinctive feature of the case.

Paul Stine, a 29-year-old taxi driver and PhD student, was fatally shot on October 11, 1969, in San Francisco. The killer sent newspaper editors fragments of Stine’s bloodstained shirt. The Zodiac’s communications began publicly on July 31, 1969, when he mailed letters containing a 408-character cipher to multiple newspapers, threatening a "kill rampage" if the code was not published on the following day's front pages. This threat prompted widespread fear, with the public and authorities responding with heightened vigilance.

Four letters containing ciphers were later sent to the press. In one letter, the Zodiac threatened violence against schoolchildren, claiming he would shoot out the tires of a school bus and target children exiting it. This led to increased police presence on school buses, although no subsequent attack occurred.

Investigations by the San Francisco Police Department, based on surviving witnesses’ descriptions, suggested the perpetrator was a white male between 35 and 45 years old, roughly 5 feet 8 inches to 6 feet tall, with ties to California. Among several suspects, Arthur Leigh Allen, a former Navy veteran and schoolteacher, drew particular attention. Allen reportedly taught students about cryptography and played a murder ballad related to the case, leading to speculation about his involvement. However, Allen’s fingerprints did not match evidence from the crime scenes. He was later arrested on unrelated child molestation charges in 1974 but was never formally charged in connection with the Zodiac murders.

Over the years, more than 2,500 suspects were investigated with no conclusive arrests or convictions. Law enforcement officials cited procedural challenges, including mishandling and poor coordination of evidence, as obstacles in solving the case.

Other suspected individuals have emerged over time, such as Gary Francis Poste, a U.S. Air Force veteran and painter whose facial scars resembled early police sketches. Various theories, including potential links to earlier unsolved murders from other regions, have been proposed by cold case investigators, but none have been definitively proven. The case remains one of the most enduring unsolved criminal mysteries in Northern California.