Zodiac ciphertexts

The "Zodiac" ciphertexts are excerpts from letters sent to newspapers in 1969-1970 by a serial murderer in the San Francisco Bay area. He killed or attempted to kill at least seven people, and possibly a number more. No perpetrator has been found, nor have the narcissistic and unhinged content of the plaintexts contributed much to the investigation. The letters include other content not shown here.


This ciphertext followed the first couple of shootings. It was split into three sections and sent to separate newspapers. It was solved by Donald and Bettye Harden soon after it was published.

ciphertext of Z408

The polyalphabetic key is below. The lack of variants for the letter 'h' in the key may indicate that he was employing a letter frequency table based on dictionary words rather than whole texts.

polyalphabetic key for Z408

After substitution, the grid appears as follows:

text grid for Z408

The plain text is as follows. The meaning of the last line is not known.

i like killing people because it is so much fun
it is more fun than killing wild game in the forrest
because man is the moat dangerous anamal of all
to kill something gives me the moat thrilling experence
it is even better than getting your rocks off with a girl
the best part of it ia thae when i die
i will be reborn in paradice snd
all the [people?] i have killed will become my slaves
i will not give you my name
because you will try to sloi down or stop
my collecting of slaves for my afterlife
ebeorietemethhpiti [?]

Some speculations. Many of the errors may be due to symbol copying mistakes (implying the letters were converted to symbols before copying into the separate grids). The 'a' and 's' can be represented by the similar filled vs dotted triangles, 'e' and 't' by the similar letters N vs H, 'i' and 'w' by an open triangle vs the letter A. The mis-spelling of 'animal', 'experience' and 'forest' and the omission of a word appear to be errors. The word 'paradise' is consistently (and maybe deliberately) spelt as 'paradice' in all of the texts from the murderer.


The second ciphertext was posted on a card following a radio interview with a mentally ill patient who had rung in posing as the killer. It was only solved in 2020 by Sam Blake, Jarl Van Eycke, and David Oranchak.

ciphertext of Z340

The polyalphabetic key is as follows. He appears to have used the same symbol to encode the letters 'k' and 'v'.

polyalphabetic key for Z340

After substitution, the letters are in a grid containing transposed text. The last lines appear to have been placed first (with some words reversed). The main section is split into two parts, and traversed in a one-down-two-across pattern. He has made a transcription error when preparing the second section, missing a letter and later adding it to the end of the line. The second section also has an inserted fragment from the third section which is skipped over.

text grid for Z340

The plain text is as follows.

I hope you are having lots of fan in trying to catch me
that wasn't me on the tv show
which bringo up a point about me
i am not afraid of the gas chamber
becaase it will send me to paradlce all the sooher
because e now have enough slaves to work for me
where everyone else has nothing when they reach paradice
so they are afraid of death
i am not afraid because i know that my new
life will be an easy one in paradice
death is life

I have assumed the fragment inserted into the middle section is from the end of the text. This then gives the concluding phrase 'death is life'. I think this fits with the overall theme of the letter, in part a reaction to the radio station caller who had said he was "afraid of the gas chamber".

Some speculations. Many of the errors could be due to letter copying mistakes (implying the letters were transposed onto the grid before being converted to symbols). These include the letter pairs 'l' vs 'i', 'a vs 'u', 'h' vs 'n'. However, this does not explain the letter 'o' vs 's' in 'brings'.


The third short ciphertext fragment was on a card, and claims to be the name of the murderer. It is too short for an unambiguous solution.

ciphertext of Z13


The fourth short ciphertext fragment was in a letter, and claims to be the location of a buried bomb, accompanied by a bay area map. It also is possibly too short for an unambiguous solution.

ciphertext of Z32