As stated, if you have identified a Zodiac suspect through other evidence and the partial DNA then provides a match, the significance of the match is more relevant than just a random match from the general population. A comparison between Zodiac letters, if all contained partial DNA profiles, would therefore be more conclusive if a match was secured, as you have a strong evidentiary reason for doing so.
Narrator in the documentary "However if Doctor Cydne Holt can find enough genetic material from Zodiac's stamps and letters, she can compare it to a wafer thin slice of brain tissue from Arthur Leigh Allen's autopsy." Dr Cydne Holt "This brain tissue from Arthur Leigh Allen is the reference sample that I would use for the comparison." Narrator "Dr Holt has already detected the possible presence of Zodiac's DNA in the seal of the envelope that contained the greeting card (Dripping Pen Card and 340 cipher), and just in case that test fails to provide a full DNA profile, she also prepares to look for DNA beneath the stamps on two of these three letters (July 31st letters)." Dr Cydne Holt "Depending on whether those DNA's match each other, might allow me to include or exclude Arthur Leigh Allen as potentially contributing the DNA on the Zodiac letters."
As she states in the last line, she must match between letters to then be sure Zodiac is the contributor of the DNA. Ruling out a suspect to just one letter is meaningless, as that letter could be from the hand of a hoaxer. But by comparing the Dripping Pen Card envelope to the first three letters mailed by the killer, she can then corroborate the DNA as likely from Zodiac, before moving on and comparing it to any potential suspect. A DNA match between envelopes must have been secured, as she followed on to exclude the three subjects in the video. This with near certainty provides a link from the Dripping Pen Card to the July 31st 1969 letters and to the killer. Second Youtube video discussing the DNA here.
The hair failed to provide a DNA sample, as the root was missing, but advances over the last 20 years, particularly regarding mitochondrial DNA may yet provide useful information.
Here is a list of envelopes processed for DNA, minus the envelopes from July 31st 1969, as they had been misplaced at the time this list was compiled. It can be noticed that the 1978 'I am back with you' letter has yielded DNA material, but is attributed as not being an authentic Zodiac letter. Since authorities now have Zodiac's partial DNA profile, it is fairly certain that this letter has now been compared and effectively ruled out, laying to rest any debate about its authenticity.
What is apparent; is that although all the preceding material, including the July 31st 1969 letters, contained the evidence of cells, there is an evident departure of any recorded biological material up to 1974 on the Halloween Card, Los Angeles letter, Pines Card, Monticello Card, Citizen Card, Red Phantom letter, and possibly 13 Hole Postcard. Admittedly many of these are postcards, hence may not have been tested or attributed on this list due to the absence of an envelope, but what we are left with, is that subsequent to the 'Little List' letter mailed on July 26th 1970, we have to wait three and a half years to the 'Exorcist' letter on January 29th 1974 for any cells to be found on the envelope again (obviously dismissing the 1978 letter).
It is quite conceivable that the 'Little List' correspondence may have been Zodiac's last, unless he willfully attached himself to the Cheri Jo Bates murder by sending the 'Los Angeles' letter on March 13th 1971.
Seasoned Zodiac researcher Mike Rodelli, featured in the ABC Primetime Investigation, stated on Zodiac Killer Site forum "The DNA on the 1978 letter is supposedly what proves that letter was NOT from Zodiac. Alan Keel, who did the early DNA testing on the SFPD evidence, told both me and LL that DNA matching the 1978 letter was found on one of the 1974 letters. We still can't find out which one, though! They are both considered forgeries. So you have to be careful, IMHO, if you make a case about a suspect that involves evidence from all four of those 1974 letters because one is the odd man out. However, one of the 1974 letters is considered a forgery AND the only letter with cells found on it from that year IS the Exorcist letter! Do I dare? It is blasphemy to suggest that the Exorcist letter is the "second forgery" because of the sacred palm print. Hey, Z never left a palm print on any other letter, so maybe that suggests that he did not write that one, either!"
If this is true, and I have no reason to believe otherwise, then one of the four 1974 letters is a fake. If we take the four correspondences; The 'Exorcist' letter, 'SLA' letter, 'Citizen' card and 'Red Phantom' letter, the most 'genuine' looking material is the 'Exorcist' letter. A hoaxer attempting to make the correspondence look like Zodiac, will attempt to copy known Zodiac letters, as shown by the 1978 letter, so in theory the 'Exorcist' letter could be considered the 'odd man out'.
Mike Rodelli added "There is *one person* (Dave Toschi) whose name has come up time and again as possibly having forged the 1978 letter, and he suffered for those claims. The presumed goal of a forger sending a letter like the 1978 letter would have possibly been to reinvigorate a dying investigation. After all, Zodiac had not written a letter since either May or July 1974. That is three years and change. When the Exorcist letter arrived, although it was not written like a true "Zodiac" letter with the correct opening phrase, it did have the effect of reviving a dead investigation once it was revealed as a "Zodiac" letter. Zodiac had not written in nearly three years at that point, so the investigation had gone a bit cold.
So the Exorcist letter can at least be construed as having had the same goal as what Keel said is a known forgery in the 1978 letter."
In fact none of the letters in 1974 opened with the line "This is the Zodiac Speaking", none were adorned with the crosshairs symbol, only one featured a running victim total and all were rather tame, truth be told, signed "Yours truly", "a friend", "A citizen" and "the Red Phantom." The final three letters in 1974 were also postmarked: unknown, Alameda County and San Rafael, along with the 1990 'American Greetings' card which was mailed from Eureka, a marked deviation from the geography of earlier correspondence.
The first letter to arrive, containing any DNA/cells, after the 'Little List' letter on July 26th 1970 was the 'Exorcist' letter on January 29th 1974 and both contained lines paraphrasing 'The Mikado', a satirical comedic opera by Gilbert and Sullivan. Strange therefore that the Zodiac should refer to 'The Exorcist' as "the best satirical comedy that I have ever seen," albeit introducing 'Tit Willow' into the letter, that this time appears to have little purpose or context. But does this validate the 'Exorcist' letter or does the three year Zodiac hiatus affect its apparent status, as the last confirmed Zodiac correspondence ever mailed by the killer. The fact it was confirmed as the final correspondence likely works in its favor.
THE ZODIAC KILLER'S DNA PART TWO