When we take a close look at the decoded 408 cipher, it can be argued that he made a fundamental error when he encoded his original message, accidentally omitting the word "people" in the ciphertext. This is explained in 'The 18 Unsolved Characters [Pt3]' This effectively created a shortfall of 6 characters in his 408 cipher, which had he not done, would only have left 12 unsolved characters at the end of the message. In view of the Bay Area murderer identifying himself as "Zodiac" just four days later, it was considered that his impatience may have compelled him to reveal his identity earlier than he would have liked, and "Zodiac" was integral to his identity in the 12 characters at the end of the 408 cipher. The hidden identity, therefore being the "Zodiac Killer".
Had the 408 cipher read "the best part of it, is that when I die I will be reborn in paradice and all the people I have killed will become my slaves", and the last 12 characters contained his identity, then by extension, we should be looking backwards to Riverside for the previous time he used a form of cryptic or hidden message. The only letter that contained such an instance, was the November 29th 1966 letter beginning "The Confession by - - - - - - - - - - - -". The Confession letter to the Press-Enterprise contained 12 underscores of, presumably, the hidden name or identity of the killer. For those believing a connection from Riverside to the Bay Area, the potential murderer of Cheri Jo Bates may have cloaked his identity behind 12 underscores in this particular Riverside Confession letter and 12 characters in his communication with the San Francisco Chronicle on July 31st 1969. The 'Bates' letters correlated via a trinity of letters, whereby the Confession letter correlated through the identity of twelve. However, the length of the underscores on the Confession letter to Riverside police appears notably longer. See here.
This analysis fundamentally fails to successfully bridge the divide from Riverside to the Bay Area, as many arguments have before - and the connection between the murder of Cheri Jo Bates and associated communications, to the Zodiac Killer, will remain a hot button topic for many years to come no doubt - but the search goes on.