First brought to our attention on Tom Voigt's message board, the photocopied keys of the Eureka card were traced by the numbers on them to a post office box and the eventual owner, who they called "Sam", but was later identified as Chester Clark Klingel who lived in Eureka. This is obviously relevant because the Christmas greeting card was postmarked Eureka, California. It has been speculated that the Zodiac Killer may have found the keys, which has some merit when you consider the Ancient Greek word of Eureka meaning "I have found". However, it's unlikely that these keys were just found on the street without the Zodiac Killer knowing the owner's identity, because the Eureka card was designed in such a way that it hinted at the name "Chester" by the contents of the card. He gave us clues to the names of Donna Lass and Kathy Snoozy in two previous cards, so why shouldn't he do it for a third time. Having noticed this possibilty, I was happy to see that somebody else had also touched on this idea on the Zodiac Killer message board, but it was sadly passed over. Nin stated "Another trivia, Chester Carlson, the inventor of xerography (xerox) spent 3 years at RCC, Riverside".
Xerox was founded in 1906 in Rochester, New York, as The Haloid Photographic Company. It manufactured photographic paper and equipment. In 1938, Chester Carlson, a physicist working independently, invented a process for printing images using an electrically charged photoconductor-coated metal plate and dry powder "toner". However, it would take more than 20 years of refinement before the first automated machine to make copies was commercialized, using a document feeder, scanning light, and a rotating drum. Chester Floyd Carlson is best known for inventing electrophotography, the process performed today by millions of photocopiers worldwide. Carlson's process produced a dry copy, as contrasted with the wet copies then produced by the mimeograph process. Carlson's process was renamed xerography, a term that means "dry writing".
How likely is it, that the not so common name of "Chester" would be the inventor of a process used by millions of photocopiers worldwide, and would be the owner of the two photocopied keys placed inside the Eureka card by the Zodiac Killer, while also living in Eureka, California in 1990. The card outer was now completed: "From your secret pal, can't guess who I am yet? Well, look inside and you'll find out". Chester. Chester Clark Klingel was ruled out as being the Zodiac Killer, so it's evident that this was just another game by the Zodiac Killer, intending to misdirect law enforcement on yet another wild goose chase. But if he knew the name of Chester Clark Klingel when designing the greeting card, it may bring us a little closer to finding out who he was.