For those who strongly believe the 1990 Eureka card is the Zodiac Killer, this is an important question. If the communications can be linked, then advocates for the 1990 Eureka card must advocate for the 2001 Happy New Year card also. It would rule out any suspects dead or incarcerated subsequent to December 1990 and up to January 10th 2001 such as Theodore Kaczynski, who was arrested on April 3rd 1996 and given eight life sentences. It would also rule out high profile suspect Arthur Leigh Allen who died on August 26th 1992. Now obviously, staunch advocates of Theodore Kaczynski or Arthur Leigh Allen, who also believe that the 1990 Eureka card was Zodiac, will almost certainly reject the 2001 Happy New Year card by default, or now distance themselves from the Eureka card if it was proved it was linked to the 2001 card. Here is a comparison between the envelope handwriting before we move on.
The 1990 Eureka card and 2001 Happy New Year card, whether Zodiac or not, were mailed eleven years apart. We are not aware of any other Zodiac or copycat communications in between these years. If there has been any, they have not been released. We have to look at these two communications in respect to all the confirmed and suspected copycat letters from 1969 to 2001 (a span of 32 years). If these two communications were not the same author (and the 2001 author couldn't have copied the 1990 author), then it is unusual that these latter two communications are both festive greetings cards, never before mailed to the newspapers by the Zodiac Killer or a copycat in the thirty-two years prior. Not withstanding the handwriting, it is also the first time the Zodiac Killer or a copycat had employed the address format of "901 Mission Street" and the numbering "94103". So we have two communications, both are festive cards, and both use an envelope address format never employed in any previously publicized letters from the Zodiac Killer or otherwise. We have to ask the pertinent question of why a copycat would attempt to look nothing like the real killer. He is effectively imitating nothing the Zodiac Killer had done previously.