bpoag

Z340Q3 is a block of ciphertext located in Quadrant 3 of the Z340 letter. The quadrants are laid out according to folds made in the paper sent to police. See here:

http://i.imgur.com/cR8ej.jpg

I chose this quadrant based on it being smaller than the others, and therefore (perhaps) easier to crack from a statistical standpoint. The fewer bytes, the better. 54, in this case.

The code makes a few assumptions about what the decrypted message contains. It assumes that at least one of about 30 or 40 "signal words" will be present. I call them signal words because they presumably represent signal versus noise -- They're long enough, and unusual enough that it would be improbable to hit upon them randomly. The code will announce a match if at least 3 of these signal words are present.

The signal words themselves are a combination of commonly-used words the Zodiac killer used in his other letters, and mispelled words he used.

I decided to focus on words that were at least 5 characters long, since four-letter words were occuring randomly fairly often.. I was getting about 20 matches per day. Admittedly, some of them were interesting, but they could all ultimately be chalked up to chance and confirmation bias on my part.

"wait bus bomb" was one of them. I took my time on that one, since the Zodiac had repeatedly referred to blowing up school buses full of kids.

[deleted]

...If you hit Ctrl-C, you will forever have to live with the fact that the very next key could have been the one, which would have landed you fame and fortune and many women. :)

lol. :)

Watch, we'll crack it, and it'll be the lyrics to the Monkee's "Daydream Believer" or something equally useless.

It's certainly possible. It depends on which school of thought you're in -- The school that says this guy was a publicity hound, or the school of thought that says he enjoyed dicking with the police. He was both.