It was probably hoped that by invoking the name of Edgar Allan Poe, the Zodiac Killer would use a technique employed by Poe in the design of his next code. The Zodiac Killer, having created two lengthy ciphers, must have known that code breakers would find it difficult to confirm a solution to such a short code of thirteen characters on April 20th 1970, so may have hinted towards an answer using material created by Edgar Allan Poe. After all, it wouldn't have been the first time.
Edgar Allan Poe's essay A Few Words on Secret Writing began with an examination of the scytale method of encryption and decoding, which can be used to reveal Zodiac's message in the 340 cipher. The essay followed up with a second encryption technique by splitting the alphabet into two sections of thirteen characters, A through M, and N through Z. It didn't go unnoticed that Zodiac used thirteen characters in his code on April 20th 1970, beginning with the ciphertext character A, and ending with the ciphertext character M. In the next section of the essay, an individual who withheld his name, provided us with the following:
"To One in Paradise" was written by Edgar Allan Poe. This poem was first published as part of the short story titled "The Visionary" (later retitled as "The Assignation"). The poem was also published under the names "To lanthe in Heaven" and "To One Beloved". The title "To One in Paradise" was used in the February 25, 1843 Saturday Musuem. This poem was written after the death of Poe's wife. He writes that she was his life and he lived for her and now he looks forward to the future where they will be together again in death. link.
The Zodiac Killer must have known that any solution to the thirteen character code on April 20th 1970 was practically unverifiable, unless the answer resided within the works of Edgar Allan Poe - and this link could be reasonably demonstrated. If the Zodiac Killer was capable of placing "One in Paradice" from a poem title by Poe into the 340 cipher, then he is capable of giving us a solution to the thirteen character code from material within the novel of "The Narrative of Arthur Gordon Pym of Nantucket". "My name is" begins the novel - and is the prelude (with dash) to the thirteen character code - so why shouldn't the answer to the Zodiac's code follow both and be the same. The solution to the thirteen character code may lie within "The Narrative of Arthur Gordon Pym of Nantucket" by Edgar Allan Poe. Or can the method used to decode the "Stonington" cipher be used to provide a solution for the April 20th 1970 Zodiac cipher.