It is practically impossible to look at the envelope of the December 1990 Eureka card from the standpoint of handwriting and determine whether this communication was mailed by the Zodiac Killer. The only way to shift the needle on its authenticity or otherwise, is to compare it to other Zodiac communications, irrespective of whether these other communications have been authenticated or not. It is possible to compare two "questionable" Zodiac communications and make a case that both are genuine. It must be remembered that the 2001 Happy New Year card mailed by somebody claiming to be the Zodiac Killer was created without the knowledge of the 1990 Eureka card, because the Eureka card wasn't made public until 2007.
The author of the 2001 card decided not to mimic any previous confirmed Zodiac communications (envelopes) that were publicly available to them, and opted to use the full newspaper address of "San Francisco Chronicle", never done previously in any Zodiac Killer communication widely accepted as genuine by the Zodiac community. However, it was done by the 1990 Eureka card author. The author of the 2001 card chose to use "901 Mission Street" on the envelope, never done previously by the Zodiac Killer. However, it was done by the 1990 Eureka card author. The author of the 2001 card chose to use the zip code of "94103" on the envelope, never done previously by the Zodiac Killer. However, it was done by the 1990 Eureka card author. The only two times a questioned Zodiac communication began with "Editor" at the beginning of the envelope, followed by "San Francisco Chronicle" were in 1990 and 2007. Both of these communications used one one punctuation, in the form of a comma after "San Francisco" on the fourth line. These were the only two communications addressed to the San Francisco Chronicle and suggested as Zodiac Killer mailings, that were festive greeting cards. So we have two festive greeting cards, beginning by addressing the "Editor" of the newspaper, with the full newspaper title of "San Francisco Chronicle", "901 Mission Street", the zip code "94103" and only one punctuation in the form of a comma after "San Francisco", who were apparently two different authors that decided to use no mimicry of earlier Zodiac communications, yet managed to copy each other in all these instances. A very strange affair indeed.
The author of the 2001 card decided not to mimic any previous confirmed Zodiac communications (envelopes) that were publicly available to them, and opted to use the full newspaper address of "San Francisco Chronicle", never done previously in any Zodiac Killer communication widely accepted as genuine by the Zodiac community. However, it was done by the 1990 Eureka card author. The author of the 2001 card chose to use "901 Mission Street" on the envelope, never done previously by the Zodiac Killer. However, it was done by the 1990 Eureka card author. The author of the 2001 card chose to use the zip code of "94103" on the envelope, never done previously by the Zodiac Killer. However, it was done by the 1990 Eureka card author. The only two times a questioned Zodiac communication began with "Editor" at the beginning of the envelope, followed by "San Francisco Chronicle" were in 1990 and 2007. Both of these communications used one one punctuation, in the form of a comma after "San Francisco" on the fourth line. These were the only two communications addressed to the San Francisco Chronicle and suggested as Zodiac Killer mailings, that were festive greeting cards. So we have two festive greeting cards, beginning by addressing the "Editor" of the newspaper, with the full newspaper title of "San Francisco Chronicle", "901 Mission Street", the zip code "94103" and only one punctuation in the form of a comma after "San Francisco", who were apparently two different authors that decided to use no mimicry of earlier Zodiac communications, yet managed to copy each other in all these instances. A very strange affair indeed.