The April 20th 1970 letter opens with "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....". One of the takeaways from the mention of his previous cipher while beginning this communication, has been that something about that previous cipher may aid in the solving of the current Z13 code. Many have taken the code key from that now solved 340 cipher and tried to apply it to the Z13 code. While some of those attempts have produced interesting outcomes, they have all required some form of manipulation to generate a desired result, which leaves room for objection. But what if the answer or key lay in the unsolved 340 cipher at the time Zodiac mailed his Z13 code on April 20th 1970. Bearing in mind this latest letter was suggesting that the Z13 code would reveal a "name" or "identity", it is quite possible that his identity in the unsolved 340 cipher held the clue.
In the 340 cipher on the final line he appeared to give us his signature of ZODIAC from characters 333 to 338. However, he replaced the "D" with a blackened triangle, reversed the "I" and "A", and changed the "C" for a "K". Despite this, it's unmistakable presence is there for all to see. What if we took this identity to solve the Z13 code.
In the 340 cipher on the final line he appeared to give us his signature of ZODIAC from characters 333 to 338. However, he replaced the "D" with a blackened triangle, reversed the "I" and "A", and changed the "C" for a "K". Despite this, it's unmistakable presence is there for all to see. What if we took this identity to solve the Z13 code.
As stated previously, Professor Donald C. B. Marsh invoked the name of Edgar Allan Poe to challenge Zodiac to reveal his name on October 22nd 1969, hoping that the Zodiac Killer would utilize the cryptographic works of Poe to create any forthcoming ciphers. Taking one look at Poe's essay, "A Few Words on Secret Writing" in the July edition of Graham's magazine, you can see the scytale method of decryption that can be used to solve Zodiac's 340 cipher, the cryptographic technique of splitting of the alphabet A through M and N through Z, which Zodiac employed in his design of the Z13 code, and the cipher wheel explained by Poe, which not only decodes the "near Zodiac" on the final line of the 340 cipher to give us the key, but provides us with a resulting key that the Zodiac placed directly into his 13 characters on April 20th 1970, that generates an answer he would later reveal as his signature on January 29th 1974. That signature was "Me".
The "near Zodiac" in the 340 cipher has simply been manipulated using a cipher wheel. When we compare the correct spelling of ZODIAC to the version supplied on the final line of the 340 cipher, we can see that Z to Z, O to O, and D to triangle generates no difference alphabetically (000). Whereas "IAC" to "AIK" generates a shift of 8 positions for each letter, producing 888. This provides us with 000888, the possible origin of the three circled 8's in the Z13 code. Visit the Caesar cipher wheel here and type in the number 8 (see below). The inner wheel will spin 8 positions clockwise so that the outer wheel "I" is represented by the inner wheel "A" (and vice versa). The outer wheel "K" is represented by inner wheel "C" (and vice versa). This is the bedrock of the switch from "IAC" to "AIK" in the spelling of ZODIAC. If we place the 13 characters from the April 20th 1970 letter within a cipher wheel (shown above), forming an inner and outer ring, and then spin the inner wheel clockwise by 8 positions, the three circled 8's land over "ME" and the "crosshairs". The signature he chose to use in the "Exorcist" letter on January 29th 1974, created by a technique described by Poe in "A Few Words on Secret Writing".
The "near Zodiac" in the 340 cipher has simply been manipulated using a cipher wheel. When we compare the correct spelling of ZODIAC to the version supplied on the final line of the 340 cipher, we can see that Z to Z, O to O, and D to triangle generates no difference alphabetically (000). Whereas "IAC" to "AIK" generates a shift of 8 positions for each letter, producing 888. This provides us with 000888, the possible origin of the three circled 8's in the Z13 code. Visit the Caesar cipher wheel here and type in the number 8 (see below). The inner wheel will spin 8 positions clockwise so that the outer wheel "I" is represented by the inner wheel "A" (and vice versa). The outer wheel "K" is represented by inner wheel "C" (and vice versa). This is the bedrock of the switch from "IAC" to "AIK" in the spelling of ZODIAC. If we place the 13 characters from the April 20th 1970 letter within a cipher wheel (shown above), forming an inner and outer ring, and then spin the inner wheel clockwise by 8 positions, the three circled 8's land over "ME" and the "crosshairs". The signature he chose to use in the "Exorcist" letter on January 29th 1974, created by a technique described by Poe in "A Few Words on Secret Writing".
But how do we know that the three circled 8's are the key to solving the Z13 code? In the April 20th 1970 letter the Zodiac Killer wrote "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....", followed by 13 characters. The next time the Zodiac used the verb "to crack", is when he told us he was crackproof in the 13-Hole postcard at the beginning of October 1970, five and a half months later. The Zodiac Killer stated "Fk I'm crackproof" and punched 13 holes into the fabric of the postcard. But just like the April 20th 1970 letter featured three circled 8's in a configuration of 13 characters, the postcard in October separated out three punch-holes from the other ten. These three punch-holes were positioned almost directly below the positions the three 8's slotted into the Z13 code (see below). In other words, pull the three 8's downwards from the Z13 code and you get the 10:3 configuration shown in the 13-Hole postcard.
Was the Zodiac Killer highlighting the three punch-holes (888) from the total of 13 to show that these were the key to solving the "crackproof" Z13 code on April 20th 1970? In total, we have the three circled 8's generated by a cipher wheel from the "near Zodiac" in the 340 cipher, placed into the Z13 code five months later, which by using a cipher wheel once again, generated the signature of "Me" from the Z13 code, that is present as the signature in the Exorcist letter on January 29th 1974. The Edgar Allan Poe essay "A Few Words on Secret Writing", featuring the cipher wheel, the scytale method of cryptography, and the technique of splitting the alphabet into 13 characters, which are all integral to the solving of the 340 cipher and the possible design of the Z13 code, may very well have been chosen because of the challenge by Marsh on October 22nd 1969. He wanted the Zodiac Killer to send a cipher to The American Cryptogram Association that would honestly include his name. The murderer of five may have given Professor Marsh more than he bargained for.
On January 29th 1974, April 24th 1978 and October 27th 1987, the Zodiac signed himself "Yours truley" or "Yours truly" as an added signature. "Yours Truly" simply means "Me". Both were used in the Exorcist letter on January 29th 1974. "Yours truly" originated as a formal sign-off for a letter, a shorter version of phrases like "I am truly yours". Today, it is mostly used in a conversational or informal context to refer to oneself in a playful, humorous, or self-deprecating manner. I believe that when the Zodiac Killer mailed the April 20th 1970 letter and Z13 code, he gave us the answer of "My name is....Me" as a playful joke. He was taking the piss.
A solution created by converting ciphertext into plaintext from just 13 characters could never be verified, which is probably why he employed a different technique, inspired by the writings of Poe in Graham's Magazine in 1841. Those three circled 8's may have stood out for a reason.
FOLLOW UP ARTICLE: THE SAME IDENTITY IN THE HALLOWEEN CARD
FURTHER READING: AN IDENTITY DISCLOSED IN TWO LETTERS
On January 29th 1974, April 24th 1978 and October 27th 1987, the Zodiac signed himself "Yours truley" or "Yours truly" as an added signature. "Yours Truly" simply means "Me". Both were used in the Exorcist letter on January 29th 1974. "Yours truly" originated as a formal sign-off for a letter, a shorter version of phrases like "I am truly yours". Today, it is mostly used in a conversational or informal context to refer to oneself in a playful, humorous, or self-deprecating manner. I believe that when the Zodiac Killer mailed the April 20th 1970 letter and Z13 code, he gave us the answer of "My name is....Me" as a playful joke. He was taking the piss.
A solution created by converting ciphertext into plaintext from just 13 characters could never be verified, which is probably why he employed a different technique, inspired by the writings of Poe in Graham's Magazine in 1841. Those three circled 8's may have stood out for a reason.
FOLLOW UP ARTICLE: THE SAME IDENTITY IN THE HALLOWEEN CARD
FURTHER READING: AN IDENTITY DISCLOSED IN TWO LETTERS
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