Jan. 5, 2010 -- Around San Francisco, the name "Zodiac" evokes darkness. Four decades have done nothing to diminish the brutality of his crimes -- five executions by bullet and blade -- or their hold on the popular imagination.
For two years in the late 1960s the Zodiac killed, taunting police in a string of letters, some encrypted, to local newspapers. Then he disappeared, leaving behind a bloody mystery that remains unsolved.
"It was scary, and the murders were real, and they were terrible -- totally innocent people killed for no reason by this psychopath," said Lance Williams, a journalist with the Berkeley-based Center for Investigative Reporting who wrote about the Zodiac crimes for the San Francisco Chronicle.
To this day, police and journalists receive tips on the murders. And there's a thriving cottage industry of enthusiastic amateur Zodiac sleuths, some of whom have devoted their lives to the mystery.
The Zodiac's first claimed murders were in Benicia, Calif., and nearby Vallejo. In both cases the killer pulled up next to a young couple parked in a car and shot them point-blank. Later he stabbed a couple picnicking at Lake Berryessa, in Napa County, and shot a cab driver in San Francisco. He often called police from pay phones to report his crimes.
"There was hysteria," said Matt Meredith, who grew up in Vallejo and now is a detective in charge of the Zodiac killing that took place in a park outside of town. "It altered people's lives."
After the San Francisco killing, the Zodiac sent a swatch of bloody cloth from the victim with a letter to the Chronicle.
"The Zodiac would write letters to the Chronicle, letters to the editor, bragging of his exploits," said Williams. "They often started by saying, 'This is the Zodiac speaking.'"
Hollywood was captivated. The 2007 film "Zodiac" spawned renewed interest in the murders and the murderer.
"Back when I was a kid, there was a rumor and talk that the Zodiac lived in a cave and don't go up in that cave," said Meredith. He produced a large police binder. "All the tips in this binder deal with the Zodiac case," he said. "But these are all tips that came in 2007."
That's when the movie came out and police had to establish a Web site for an avalanche of tips. Meredith still gets at least one a day.
"I see every tip," he said. "I read every tip. Some of them are ridiculous. Some of them are compelling, for lack of a better word, but I read every one."
'I Met the Zodiac'
Williams still gets tips too, every time he writes a story about the Zodiac. "There's a flurry of contacts from people all over the place who think they've solved it," he said. "They range from 17-year-old boys to retirees. We've heard from people from all over the world, not just in the Bay Area. ... It's San Francisco's all-time unsolved murder mystery, even though only one of the murders was actually in San Francisco."
Williams has kept many of the letters and e-mails. Some point to family members. "For many years now," reads one letter, "I have been researching the possibility that my husband of 20 years was indeed the killer." Other tipsters claim to have broken the killer's mysterious code. "I decoded one of his ciphers that reveals his full name," one tipster wrote.
And then there are the letters that recount close encounters with the killer. "I met the Zodiac inside a dark bar in California in 1974 and we talked face-to-face for three hours," reads one letter Williams received.
The journalist speculated on the tipsters' motivation. "They want someone to publicize the fact that they've solved the crime and so forth," he said. "The problem is all the solutions are different, and there can only be one."
Uncovering the Zodiac killer's identity has become a holy grail for a dedicated band of amateur sleuths. Over the years, thousands have taken up the hunt. "Nightline" went hunting with a few of them, none more memorable than Dennis Kaufman. For him, unmasking the Zodiac is not a profession but an obsession.
"I realize that a lot of people have come forward and claimed to know who the Zodiac is," said Kaufman. "That makes it very difficult for me because the bottom line is, I really do know who the Zodiac is."
Amateur Sleuths Track Zodiac
Kaufman is convinced his late stepfather, Jack Tarrance, was the Zodiac killer. For the last decade, Kaufman has collected what he claims is proof. It's a dizzying presentation. There are photographs, handwriting samples, even physical evidence.
"This stuff could be usable evidence," Kaufman said.
Cheri Jo Bates was stabbed and nearly decapitated in 1966. Kaufman believes she might have been one of the Zodiac's first victims. And he thinks he might have the murder weapon: a knife that had belonged to his stepfather.
"The main thing in this thing is this knife," said Kaufman, displaying the blade. "This could be very well be the knife that killed her."
Why hasn't he turned the knife in to police yet?
"They told me to hang on to it," he said. "They might want it at a later date."
Kaufman has turned over a black hood he contends belonged to his stepfather. A survivor described the Zodiac wearing such a hood during his attack.
"The FBI is in possession of this hood now," said Kaufman, displaying a photo.
He admitted frankly that the case has taken most of his time for years.
"Nine years," he said. "I can honestly say that I've spent almost every awake moment of my life, every penny that I've got, everything went into this case. ... I can't even add it up. Everything I've made beside what I eat and pay my bills with has went into this case."
He said it's not just financial costs, but "the energy that it takes just to keep going."
"When I hear the word 'Zodiac,' it's like I want to go down and go to sleep because it drains me that bad." Kaufman said. "This case will probably be with me for the rest of my life until I die. But hopefully I can do something else in life before I am dead."He said he would not let it go until the solution was found.
"It has to be solved," he said.
Many Zodiac hunters have focused on the cryptograms the killer left behind, convinced the ciphers contain clues to his identity. Emanuel Segal, a teacher with a talent for word games, spent months decoding one of those messages. He explained his method.
"This is the string of 18 letters that he gave us..." Segal said. "These are the letters and the missing words that I figured out needed to be there. OK, so I couldn't put it on one line, but it was too long, but the S-Ts are the correct letters, S-T, it should have been an S, it should have been a T."
Segal thinks he knows who the Zodiac is.
"I do think it's Ted Kaczynski," he said.
Theodore Kaczynski, the Unabomber. Not a new theory, but one, Segal says, that makes sense.
"Sometimes people can get lucky, taking a fresh look at something," he said. "You have all these experts who are looking at it in a certain way, and they are great. These are the top people in the world and there's no slight to them at all that they haven't figured it out."
Despite all the theories and tips, the Zodiac's trail grows colder with each passing year. But that has not dampened the allure of catching him. And who knows? He may still be out there, hidden, watching as a new generation joins the hunt.
"There'll be someone else behind me to pick up the case," said Meredith. "And it'll be, to some degree, there'll always be someone that's there to either take the phone call or open the letter."