These complex cryptograms are extremely difficult to solve because of the excessive ciphertext characters used in the encoding process. However, there are some possible openings. The Zodiac Killer mailed a 408 character cipher on July 31st 1969, a 340 character cipher on November 8th 1969, a 38 character cipher on December 7th 1969, a 13 character code on April 20th 1970 and a 32 character code on June 26th 1970, but not once did he use the "sun cross" or "number 7" as a ciphertext character. The 148 character cipher mailed to the San Francisco Chronicle by the Zodiac Killer sometime in May 1971, the 50 character cipher mailed to the Albany Times Union newspaper on August 1st 1973, and the 180 character Scorpion cipher mailed in 1991 (all bearing traits of the Zodiac Killer and not contemporarily published in the newspapers), all contained the "sun cross" and "number 7" as a ciphertext character. The "number 7" in the 1971 and 1973 ciphers, both decoded to the plaintext letter "A".
In the 148 character cipher mailed in 1971, the Zodiac Killer used the "sun cross" as a signature rather than his traditional crosshairs - thereby signing off his communication with the letter "Z" - because the "sun cross" descoded to the plaintext letter "Z" in the 148 character cipher. Bearing in mind that the Scorpion letter author headlined with the wording "Hi, Remember Me", it had to be considered that the pseudonym "Zodiac" may have been hidden somewhere in the cryptogram. Since the Zodiac Killer probably used the "sun cross" to represent the letter "Z" in the 148 character cipher, I took a look at the 180 character Scorpion cipher to see if any repeating ciphertext characters would mimic the pseudonym "Zodiac", using the "sun cross" to represent the plaintext letter "Z". Below are the examples I found beginning on row 2 and 14. To view the Scorpion letters and ciphers, please visit Science Blogs.