Mike tackles this problem in extensive detail, particularly with regards to the viability of the DNA tests conducted by Dr. Cydne Holt in the 2002 ABC Primetime documentary, in addition to his discussions with Alan Keel, Criminalist at the San Francisco Police Department, San Francisco, California from 1996 to 1999.
The disputed results of the 2002 'showpiece' are now well documented, however, Mike delves further into the DNA analysis with respect to two later 'Zodiac' letters, namely the 1974 'Exorcist' letter and the subsequent 1978 'I Am Back With You' letter, both mailed after a lengthy silence from the Zodiac Killer - leading some to question their authenticity.
Mike recalls information of his conversation with Alan Keel: "In contrast (to earlier communications), Keel analyzes two other letters, one of which is the 1978 forgery, and finds that this letter and one of the 1974 letters are loaded with saliva and cells. He then easily extracts DNA from both of these letters using the more primitive DNA technology of that time and finds that the DNA matches between those two letters, thus proving that one person sent both."
This is a stunning revelation (if correct) when we consider the findings of the San Francisco Police Department laboratory in the 1990s, in which there was a notable absence of saliva/DNA present on the envelopes prior to the 1974 'Exorcist' letter. Would a killer who seemingly didn't lick any of his envelopes or stamps throughout the majority of his letter-writing campaign, now suddenly break that habit in the 1974 and 1978 communications? The SFPD report, shown here, references the April 24th 1978 letter, claiming that the "DNA SAMPLE OBTAINED - NOT AUTHENTIC ZODIAC LETTER".
This lack of saliva or DNA on the earlier letters may have become more evident, as Dr..Cydne Holt struggled to generate any tangible results from the sealed sections of stamps and envelopes using more advanced forensic DNA testing in 2002, compared to the earlier and more primitive testing undertaken in the 1990s. This apparent dichotomy brings into stark reality the essence of Mike Rodelli's argument.
"DNA sample obtained- not authentic Zodiac letter" could imply they know the sex of the DNA present on the 1978 letter, and therefore by extension, not the Zodiac Killer (as suggested on many forums). But, it could imply they know the identity of the individual who contributed the DNA to the 1978 letter, and having identified that individual, know they were not the Zodiac Killer. This lack of clarity has led Zodiac researchers to question the transparency of the San Francisco Police Department.
We know that a partial DNA profile from a letter can exclude suspects, but not definitively identify an individual. Therefore, the apparent (but unconfirmed) revelation of Alan Keel that "DNA matches between" one of the 1974 letters (possibly the 'Exorcist' letter) and 1978 'I Am Back With You' letter, would suggest that full DNA profiles have been obtained for both letters.
If only a partial DNA profile had been obtained from the 1978 letter (much like the exclusion of suspects) it can only be excluded as matching a profile from the 'Exorcist' letter (if this had a full DNA profile), but not definitively matched to it.
As such, the statement of "DNA matches between those two letters, thus proving that one person sent both", would be indicative of a full DNA profile obtained from both the 1974 and 1978 letters in the 1990s..
For those who believe the 'Exorcist' letter to be genuine Zodiac correspondence, then this could imply that a full DNA profile may exist for this letter (or one of the 'lesser' 1974 letters), and consequently the profile of the Zodiac Killer. However, the search for Zodiac's DNA in 2002 negates this premise - unless the San Francisco Police Department knew all along that both the 'Exorcist'/74 letter and 1978 letter were not mailed by the Zodiac Killer. In fact, the Exorcist and April 24th 1978 letters were the only two communications mentioned with regards to the controversy surrounding Inspector David Toschi, who led the investigation for many years. He came under suspicion for forging the 1978 letter, after the San Francisco Chronicle columnist and author, Armistead Maupin, discovered that David Toschi had mailed fictitious fan mail to a series he had written, with the inclusion of the detective.
Armistead Maupin had first met David Toschi in 1976 while he was writing the 'Tales of the City' series. Wanting to energize the series with a murder mystery element, he contacted San Francisco Chronicle reporter Bob Popp, who then introduced him to David Toschi. The police inspector would make a debut appearance in 'Tales of the City' on September 10th that year, with a character based on his attributes. Further episodes would follow under his real name, as a friend and confidant to Armistead Maupin's fictitious Detective Inspector Henry Tandy.
The fact that Inspector David Toschi was questioned regarding these two communications, only heightens the mystery surrounding Alan Keel's statement of "the DNA matches between those two letters, thus proving that one person sent both" and the San Francisco Police Department's report concerning the 1978 letter, in which it noted that a "DNA sample was obtained, but indicated it was not an authentic Zodiac letter".
We don't know for certain that Alan Keel is referring to the 'Exorcist' letter when he stated "one of which is the 1978 forgery, and finds that this letter and one of the 1974 letters are loaded with saliva and cells". However, since the 'Exorcist' letter for the large part has been widely regarded as the last confirmed correspondence mailed by the Zodiac Killer, as opposed to the other 1974 communications, it would be the logical correspondence to test for Zodiac Killer DNA when searching for the Bay Area murderer. Testing the other much more questionable 1974 mailings would not make as much sense - which is probably why the San Francisco Police Department report is blank or omitted next to these communications.
The 'go to' mailing, when testing for Zodiac DNA from the 1974 letters, would undoubtedly be the 'Exorcist' letter rather than its dubious companions. So, if this was the case and the statement of Alan Keel were true, then the 'Exorcist' mailing would not be an authentic Zodiac correspondence - and as a result - would quite possibly shrink the Zodiac reign by nearly three years.