On October 29th 2021, Mike Rodelli stated on the Zodiac Killer message board "The fact remains that in 2007 Keel told me, as he had told Lafferty before me, that there is a 1974 forgery based on DNA and the ONLY 1974 letter that had been tested for the presence of cells during Keel's tenure (as demonstrated by the DNA chart that I believe Keel made in about 2000) was the Exorcist letter. This is not rocket science. Even if it is not the Exorcist letter that Keel was talking about, it IS a candidate as being a forgery whose DNA matches the 1978 letter based on the information in the chart".
In his book, The Hunt For Zodiac, he stated "Now there was DNA proof that whoever had penned the April 1978 letter had also penned one of the 1974 letters. And apparently it was not Zodiac. According to the chart of DNA testing results compiled by SFPD's lab in ca. 2000, the only one of the 1974 letters that had been tested by Keel up to that time was the January Exorcist letter. This was the letter that had a swarm of palm prints on it. This created an interesting dilemma that lends credence to the possibility that this is a forged letter. Zodiac had penned a dozen letters prior to writing the Exorcist letter and had never left even a single palm print on them. So why had he suddenly and carelessly taken off his glove(s) to write this one and leave a virtual montage of his palms all over it. From that standpoint alone, it makes sense that someone else may have written the Exorcist letter, its bizarre content notwithstanding. While it is possible that one of the other three letters was tested for DNA subsequent to the compilation of the DNA summary chart that Keel had assembled, I believe that on balance the most likely candidate for being the 1974 forgery is the Exorcist letter until proven otherwise". Mike Rodelli is almost certainly correct that the 1974 Exorcist letter is overwhelmingly the most likely DNA match for the 1978 letter (because it was the only tested in the DNA chart), but here is the almost certain proof that neither the 1974 Exorcist or April 1978 letter were forgeries.