The Zodiac Killer

The card to Avery was widely considered a threat on his life, and the Chronicle ran a front page story about it on October 31. Among the mail that this generated was an anonymous letter from Riverside urging Avery to investigate a link with the still-unsolved Bates murder. Graysmith transcribes it in ZODIAC:

Please forward the contents of this letter to the detective in charge of "The Zodiac Murder Case." I hope this information will also help you, as we would both like to see this case solved. As for myself, I wish to remain anonymous and I know that you will understand why!

A few years ago in Riverside, California, a young girl was murdered, just about, I believe, on "Halloween" evening! I could write a much longer letter, citing the similarities between Zodiac's case and this murder, which occurred in Riverside but if the police department cannot see said comparative similarities between these two cases, then I will take a "slow boat to China," even if these two crimes were committed by two different people! I think, after all the facts are studied, regarding both of these cases, if police have not already investigated these possibilities and are not already aware of the "Riverside case," then, even so perhaps they should look into it....

Letters to newspapers, "similar erratic printing" find out about these two different cases ....Give Captain Cross a call on the phone, he knows that "I do not quit."

Mr. Avery, I will give you a call in the near future, please look into the case, the Riverside police have a wealth of information, so does San Francisco, let us hope that they are not too proud to work together, and if they already are, let us hope that there has been an exchange of information....

After locating a year-old letter from the Riverside Chief of Police to a Napa County detective that had similarly linked the Bates murder with the Zodiac, Avery visited the Riverside police and reviewed their evidence.  Intrigued by the letters sent to the police and press, not to mention what appeared to be a "Z" used as a signature in some, he instigated a meeting between their detectives and detectives from Solano, Napa, and San Francisco counties, who compared notes on the Bates murder and each of the known Zodiac attacks up to that point.  Authorities from Northern California, particularly SFPD Inspector Bill Armstrong, felt that there was a link between the Bates murder and the Zodiac crimes, and that they were most likely committed by the same man.  State handwriting analyst Sherwood Morrill checked the writing on the desk and envelopes against the killer's letters to the Chronicle and found that they were "unquestionably the work of Zodiac". ¹  Riverside police, particularly Capt. Irvin Cross, were less certain and "reaffirmed [their] skepticism", ² probably because they had not released the full details of the crime to their counterparts upstate -- the number of stab wounds received by Bates, strongly suggesting what is known as a "rage killing," was not announced publicly until May of 2000.  The Riverside story broke on November 16, 1970, when Avery's article was printed in the Chronicle.

The official position of the Riverside Police Department and most independent investigators as of 1998 is that Cheri Jo Bates was not a Zodiac victim.  RPD maintains a local man as their suspect, and considers the Zodiac murders entirely unrelated, though they do concede the possibility that the Bay Area killer authored one or more of the letters sent in southern California.