I’m always interested in solving the unsolved mysteries (Murders, Space, Ciphers, Medicine).
Anyway, I’ve been looking at the Z340 Zodiac letter and how it’s already partially solved, I’ve been studying the letter and here are my thoughts relating to it
Some of the letters look like they would be in a PigPen Cipher
The Zodiac killers letter seems to be using a mixture of plaintext + encoded text, or at least 1 the entire full work + one ciphered word (or at least the ones that are easy to guess, the more detailed information is already encyrpted plus their words (accounting for spelling mistakes) also have one or two letters in the string encoded, or swapped around & encoded
They’ve linked periods to full stops to end sentences.
Examples from the first line
HER> = Here
TGOB = Both (
DWY = Day
Also near the end they’ve written POSHT = Poshtwats?
That’s my theory, so it’s what I’m working with at the moment
UPDATE : 27/07
Finding some interesting strings of words that make up a fuller story. Currently playing around with them. As the answer doesn’t match the solution already posted for about the first 8 lines