It is one of the most grisly murder mysteries of modern times, which inspired countless films and television dramas, terrorised a generation of hormonal teenagers, and has stumped detectives and amateur sleuths for more than 40 years. Now a middle-aged estate agent from California has stepped forward to claim she is the daughter of the famous "Zodiac killer".
Deborah Perez says her late father, Guy Ward Hendrickson, was responsible for at least two of the five deaths formally attributed to the notorious figure, who shot or stabbed courting couples as they canoodled in cars.
She said she was going public to "right his wrongs," and claimed to have witnessed two of the frenzied murders. She also announced that she has a pair of spectacles taken from the Zodiac killer's final victim, Paul Lee Stine.
In a further unique twist, Ms Perez even said she had helped her father scribble some of the killer's infamous confession notes, in which he taunted police, newspapers and amateur sleuths with elaborate ciphers and riddles, claiming responsibility for 37 deaths.
"I was a child and just thought I was helping my dad," claimed Ms Perez, 47, one of six children adopted by Hendrickson, who died in the 1980s. "I didn't know. He told me he was sick, and all I wanted to do was help my dad ... He kept telling me he was sick and he killed many, many people. I had no idea."
She was speaking at a surreal press conference outside the offices of the San Francisco Chronicle, one of the newspapers that received several of the letters, on Wednesday afternoon. It was attended by journalists and Zodiac enthusiasts holding photos of suspects.
Local police, who have never closed their investigation, said: "We get a significant number of calls a year," said Sergeant Lyn Tomioka. "We look into whatever evidence is presented to us."
The development will open yet another chapter in a case which has fascinated Hollywood for decades, providing the loose inspiration for the Clint Eastwood hit Dirty Harry and the hit 2007 thriller Zodiac, among others.
The "Zodiac killer" first struck in 1968, when he shot high-school students Betty Lou Jensen and David Faraday in a "lovers lane" in the city of Benicia. He was blamed for a string of further attacks, and became famous for sending cryptograms to newspapers which allegedly contained his identity.
Until now, most people have believed the self-styled serial killer was Arthur Leigh Allen, a convicted child molester who died in 1992. Police were never able to find conclusive evidence.
However Ms Perez says she was with her father when he carried out the second attack in the early hours of 5 July 1969. That saw Darlene Ferrin, 22, and Michael Maggeau killed by shots into their car, parked at a golf course in Vallejo, north of San Francisco.
"My father grabs his gun, goes to the passenger side and I hear shots, I hear moans, I hear screams," Ms Perez said. "We leave and we're pulled over by police. My father takes the gun and puts it into a bag and sticks it into my pants and says, 'Don't move. The police will not understand if they find this gun.' "
Ms Perez explained her failure to previously come forward by saying that she had been oblivious to the case until 2007, when she saw a sketch of the killer on America's Most Wanted and started to think her father was involved.
But others at the press conference suggested it had more to do with a documentary about her that is in the works. Ms Perez denied it, saying: "I am just coming forward to tell the truth."
However, a local man has stepped forward to claim his stepfather was the Zodiac killer – and a documentary is set to appear about him.