To date, the San Francisco Police Department has found only a faint result in DNA testing on the three envelopes newly discovered by the Primetime source. But the partial profile found on one of the envelopes that was already in the department's files — one containing a card sent on Nov. 8, 1969 — does allow investigators to draw some conclusions.
Click here to read the card.
"I found a partial DNA fingerprint from a male individual who — at some time — has had contact with the stamp," said Dr. Cydne Holt, supervisor of the department's DNA lab. Investigators are working on the assumption that the man who licked the stamp was the Zodiac Killer.
Holt found four out of a possible nine DNA markers, plus an indicator of gender confirming that the killer was a male.
"It's not enough to positively identify anyone as Zodiac … but it is enough to narrow suspicions, or perhaps even eliminate suspects," she said.
Next, Holt compared the Zodiac DNA with samples provided by Primetime from three men who have been identified by amateur investigators as possible Zodiac candidates. She immediately eliminated two of the men as possible matches for the Zodiac DNA: Bay Area schoolteacher Arthur Leigh Allen, who died in 1992, and a prominent San Francisco lawyer who is still living.
The third sample, from Charles Clifton Collins, who died in 1993, required a closer examination, but Holt was ultimately able to confirm that it did not match the DNA found on the Zodiac envelope.
Collins' son, William Collins, who had suspected a connection between the Zodiac Killer and his father when he saw the Zodiac's handwriting, was relieved. "Not the guy, huh? This is a good thing in my life," he said.
While the Zodiac's partial DNA profile will enable the San Francisco Police Department to eliminate some of the possible suspects from its list, it will not be enough to confirm an identification. Solving the Zodiac killings will require more evidence.
Looking for a Torn Shirttail
One piece of evidence in which investigators are especially interested is the remains of the shirttail the killer took from taxi driver Paul Stine. The killer cut off a large piece of it, but mailed only three small swatches to newspapers, raising the possibility that the remainder still exists.
"Do I think it's still out there? I want to believe it's still out there. And actually, I do think it's still out there," said Inspector Kelly Carroll, one of the investigators on the case.
Although the Zodiac Killer hinted at suicide in his last confirmed letter dated 1974, Carroll believes it is possible he is still alive.
Click here to read the latest letter from 1974.
"He would probably be in his 60s," he said. "I know that if he is [still alive], he's got to be a little more uncomfortable about the fact that the police have taken one step forward — one step closer to catching him. And I hope he's worried if he's watching."