It has been widely shown that the Z32 and Z13 codes are simply too malleable - one is too short and open to thousands of different interpretations, while the other has 29 unique characters within a 32 character code, allowing amateur sleuths to literally fill in the blanks, make it say whatever they want and subsequently justify that solution with an explanation of biblical proportions which could never be proved or disproved. I am sure that the overwhelming consensus of experts in the field of cryptology, is that without a key to the Z32 and Z13, two of the remaining three "unsolved ciphers" are effectively unsolvable. It becomes plainly evident that no such key exists subsequent to April 20th 1970 with respect to the 45 unsolved characters. The following communications have no content pertaining to a key for either the Z13 and Z32, especially when you look at the remaining communications mailed by the Zodiac Killer in 1970. If these two codes cannot be truly solved because of their brevity and character make-up - and the Zodiac Killer provided no key - then the only option remaining is he provided us with the answers. If these answers were provided in 1970, what are the odds that they would be contained in three consecutive communications, the answers would be in the exact words of Zodiac, and each would pertain to each cipher in reverse chronological order? The answer to the Mount Diablo code provided by the Little List Letter on July 26th 1970, the answer to the '13 Symbol' Cipher provided by the '13 Hole' Postcard on October 5th 1970 and the answer to the 340 Cipher provided by the Halloween Card on October 27th 1970. I won't expand any further on this because I've covered it extensively in this article and the link at its foot.
The Zodiac Killer mailed copious communications to the newspapers showing us his willingness to engage with the San Francisco Chronicle and the investigators chasing him. His literary verbosity fell from his dripping pen throughout his campaign of terror from 1969 to 1971, eager to prove he was the killer of five in the Bay Area through a succession of boasting communications. Yet this model of the Zodiac Killer is totally abandoned when it comes to his ciphers - we now have a killer who has stayed deathly silent on the workings of his codes for upwards of 50 years, unable to provide us with a single clue to their construction. A murderer who provided us with extensive details to his Lake Herman Road and Blue Rock Springs attacks, his recollections in Presidio Park, as well as finding the time to write on a car door, but has since remained astonishingly reserved and tight-lipped regarding any of his codes to this day. He has supposedly been able to resist this temptation for a possible five decades, squashing his hands and pen firmly under his buttocks in order to prevent the ink flowing from his previously rampant pen. From everything we have learned about the Zodiac Killer, could a murderer who spent more time writing than killing, just shut up shop and keep us guessing for just over 50 years?
Why do we need to play mathematical games, create anagrams, twist like a pretzel, jump through hoops, bang square pegs into round holes and create convoluted essays describing how we arrived at the solution we did, when the answer had already been given to us 50 years ago. Sometimes the answer to something doesn't require an abstract, mind-bending solution - sometimes it doesn't require a solution at all. "In the decades since, experts and amateurs have tried to crack the Zodiac's cipher, but the puzzle remains unsolved" - and will remain so until you heed the words of Zodiac. He may have been a ruthless killer, but he had loose lips and an even more loose pen.
Regardless of my thoughts, the podcasts by Michael Butterfield make interesting listening with excellent conrtributions from a number of people - and well worth the time spent to brush up on the cryptological aspect of the case.