Obviously, Zodiac researchers who specialize in the ciphers rather than the crimes themselves, have a vested interest in wishing the cipher to be a hidden message. This is the belief that keeps the dream alive.
But did the Zodiac Killer really have the ability to create a more difficult cipher than the 408, with a reasonable expectation of a solution. Placing 29 unique characters into a 32 symbol cipher, and creating a 13 symbol code would suggest not.
The October 22nd 1969 Examiner newspaper article by Will Stevens, laid down a challenge to the Zodiac Killer from the president of the American Cryptogram Association (ACA), Professor D.C.B. Marsh, to reveal his name. This may be the article that inspired the 340 cipher, and by association, the 'Halloween' card mailed approximately one year later.
"Dr Marsh told the Examiner today: "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allen Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name-in cipher code-would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code, which will truly and honestly include his name."
This contention is probably true- that the Zodiac Killer wouldn't reveal his name in any cipher (other than his pseudonym), and additionally, he likely used the fact "that any cipher created by man can be solved by man" as a springboard to create something extra special, other than a cipher. If we contend that the Zodiac Killer wrote his final letters in 1974, then is it likely that a killer touted as an attention seeker, could resist dropping us clues to the 340 cipher in his subsequent letters, spanning in excess of four years.
Each and every one of his final three communications in late 1970 and early 1971 effectively told us he was crackproof. The upside down text on the October 5th 1970 'Pace' card stated "Fk I'm crackproof." The October 27th 1970 'Halloween' card proclaimed "sorry no cipher." The March 13th 1971 'Los Angeles' letter boasted "Like I have allways said, I am crack proof." But the Zodiac Killer hadn't always said he was crackproof- only in the two communications either side of the 'Halloween' card announcing "sorry no cipher." The suggestion he was crackproof, thereby not arising from his perceived ability to evade police, but from his smugness in knowing he created three ciphers he knew would never be solved.
In view of the "by knife" attribution on Bryan Hartnell's car door, it is arguable that the Zodiac Killer had the Tim Holt comic book or Rota Fortunae (Wheel of Death) in mind as he wrote on the car door. In other words, the concept predated the September 27th 1969 Lake Berryessa stabbings, rather than just the 'Halloween' card. The Lake Berryessa "by knife" attribution becoming the part inspiration for the complex puzzle of the 340 cipher.
The "by knife" method of death (on the right) is clearly the only one falling within its quadrant, as opposed to the others, which are all connecting with the central column.
This method of death was certainly prioritized by the Zodiac Killer, having placed it on Bryan Hartnell's vehicle (despite the fact the crime was obviously committed with a knife). The feasible presence of "by knife" within the 340 cipher. The possibility of a crude 'Halloween' card design in the December 16th 1969 'Fairfield' letter featuring "death by knife," along with the "Bleeding Knife of Zodiac" drawing. And finally, the 'October 27th 1970 'Halloween' card design and comic book, both containing "by knife" and mirroring the 340 cipher and 'Fairfield' letter.
Below are the speculative beginnings, attempting to interweave the '13 Hole' postcard into the emerging design.