The Zodiac's confirmed attacks spanned ten months and four locations across the Bay Area. On December 20, 1968, he shot and killed David Faraday, 17, and Betty Lou Jensen, 16, as they sat parked on Lake Herman Road in Benicia. On July 4, 1969, he shot Darlene Ferrin, 22, and Michael Mageau, 19, in the parking lot of Blue Rock Springs Park in Vallejo. Ferrin died; Mageau survived despite multiple gunshot wounds. On September 27, 1969, at Lake Berryessa in Napa County, the Zodiac appeared in a hooded costume emblazoned with his crosshair symbol and stabbed Bryan Hartnell, 20, and Cecelia Shepard, 22. Hartnell survived. Shepard died two days later. On October 11, 1969, the Zodiac shot and killed taxi driver Paul Stine, 29, in San Francisco's Presidio Heights neighborhood, taking a swatch of Stine's shirt as proof. Each attack was different in method, location, and victim profile, a pattern of unpredictability that made the killer nearly impossible to profile.

What made the Zodiac case singular was not the body count but the correspondence. Between 1969 and 1974, the killer mailed over twenty letters to newspapers, police, Chronicle journalist Paul Avery, and attorney Melvin Belli. The letters contained details only the killer could know, swatches of a victim's bloody shirt, bomb diagrams, and escalating claims. He said he had killed seven people. Then thirty-seven. He threatened to shoot out the tires of a school bus and pick off the children as they fled. Four of the mailings included cryptograms. The first, a 408-symbol cipher split across three newspapers, was solved within a week by a Salinas schoolteacher and his wife. It contained the chilling declaration: "I like killing people because it is so much fun." The 340-character cipher, mailed in November 1969, defied cryptanalysts for fifty-one years before an international team of codebreakers cracked it in December 2020.

The Zodiac left fingerprints at the Stine murder scene. Three teenagers watched him wipe down the cab from a window across the street. A police dispatcher broadcast the wrong suspect description, and two officers who encountered a man matching the corrected description near the scene let him pass. Despite this near-miss and the physical evidence, the case produced no arrest. San Francisco Police Department detectives Dave Toschi and Bill Armstrong led the investigation for years, chasing leads that multiplied faster than they could be eliminated. The SFPD estimated it investigated 2,500 suspects over the life of the case. Only one was ever publicly named: Arthur Leigh Allen, a former elementary school teacher and convicted sex offender. Allen denied being the Zodiac. DNA evidence later appeared to exclude him, though the sample's reliability has been questioned. Allen died in 1992 without being charged.

The unsolved ciphers became the case's most durable feature. The Z408 was solved in 1969, but the Z340 resisted every approach, from hand analysis to supercomputers, until 2020, when David Oranchak, Jarl Van Eycke, and Sam Blake discovered the cipher used a complex transposition scheme that read diagonally across the grid. Its decoded message was anticlimactic: more taunting, more boasting, no name. Two shorter ciphers, the Z13 and Z32, remain unsolved. Cryptologist Craig Bauer proposed that the Z13 might encode "Alfred E. Neuman," the Mad magazine mascot, a theory that captures the frustrating blend of menace and absurdity that defined the Zodiac's communications. Amateur codebreakers and armchair detectives continue to propose solutions, suspect identifications, and theories, keeping the case alive in a way that few other unsolved crimes have managed.

The San Francisco Police Department marked the case inactive in 2004, then reopened it in 2006. The California Department of Justice, the FBI, and the sheriffs of Napa, Solano, and Vallejo all maintain open case files. The locations of the attacks remain ordinary places: a roadside turnout in Benicia, a parking lot in Vallejo, a lakeshore in Napa County, a residential block in San Francisco. Nothing marks them except the knowledge of what happened there. The Zodiac killed at least five people and terrorized a region. He wrote letters that were equal parts confession, puzzle, and performance. He signed them with a crosshair symbol and vanished. More than fifty years later, the symbol is recognized worldwide, the ciphers draw new solvers every year, and the case file remains open, waiting for a name to fill the space the Zodiac left blank.