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."
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.