This story originally ran on October 17th, 2002. The Zodiac Killer who terrorized San Francisco three decades ago with coded messages and taunts to police has never been found. But now new technology — DNA testing techniques he could not have imagined in 1969 — could be the killer's undoing.
No physical evidence identifying the Zodiac Killer was found at the scenes of his crimes, but the 20 or so letters and cards he sent to the press raise the possibility that he did leave some trace of himself: Today's highly sensitive DNA tests can extract a genetic fingerprint from saliva used to lick a stamp or seal an envelope.
In the 33 years since the killings, the San Francisco Police Department has amassed enough evidence and leads to fill an entire filing cabinet. Today, fewer than half of the envelopes sent by the killer remain, the rest having disappeared during three decades of handling by hundreds of local, state and federal investigators.
The department's DNA testing unit is testing the envelopes using a DNA technique known as polymerase chain reaction, or PCR, which can develop a genetic profile from as few as 50 human cells. A genetic profile would allow investigators to search for a match among the hundreds of thousands of genetic profiles of known criminals in national databases — as well as among the possible suspects listed in the department's Zodiac files.
The lab has found a partial DNA "fingerprint" on one of the envelopes, but not enough for definitive matching. However, a Primetime investigation prompted the discovery of three envelopes that offer new hope. The envelopes were thought to have been lost, but an anonymous Primetime source — a long-retired investigator — found them, in mint condition, during a search of his personal files and turned them over to the San Francisco police.
"The potential is exciting," said Dr. Cydne Holt, supervisor of the San Francisco Police Department's DNA lab. "If there are cells on those envelopes, we will get the DNA from them and get an answer. … The prospect of being able to contribute to the story is exciting."
Letters and Coded Ciphers
The Zodiac Killer hit the headlines in the summer of 1969, at the height of the hippie era, when San Francisco was an epicenter for the counterculture movement.
On July 31, 1969, the killer mailed letters to three area newspapers claiming responsibility for two attacks on young courting couples, one earlier that month and one the previous December. Both victims died in the first attack; in the second, the woman died but the man survived.
"Dear Editor, This is the murderer of the 2 teenagers last Christmass at Lake Herman & the girl on the 4th of July near the golf course in Vallejo. To prove I killed them I shall state some facts which only I and the police know," read one of the letters, to the San Francisco Chronicle.
The letters, written with a blue felt-tip pen, described the exact numbers of shots fired, what the victims were wearing and in what position they died, and even the brand of ammunition used in both attacks — information that had not been publicly released.