Hi everyone,

I wanted to share some of my findings regarding my work on Z13.

To begin, I must address the unicity distance problem, and the fact that multiple possible solutions exist for this cipher.

To account for this, I decided that I needed a list of all adult male names that lived in Vallejo between the years 1968-1969.  The list of possible names must be constrained to people that we know lived in the relevant area, during the relevant time period.  

I was able to obtain a scanned copy of the Vallejo 1968-1969 city directory, and OCR’d all of the names, and addresses.

I then augmented this list with common nicknames.  For example a name list as a “Robert Smith” in the city directory may also lead to entries for Bob Smith, Rob Smith, ect.  

I then took this list of names, and created another list that formats them differently.  For example, a name such as Robert A. Smith, might be tested in the forms Robert A Smith, Rob A Smith, Rob Smith, R Smith, ect.  We are testing all plausible ways of writing the name.

With this final list, names that do not meet the symbol repetition patterns of the cipher are structurally rejected.  This greatly narrows the list.  Then come the positional constraints of the cipher text symbol.  These are incredibly restrictive, rejecting every name in the city directory.

And so, I tested all of the names that meet the symbol frequency constraints using as many basic transposition steps as possible.  Now I am starting to get very close matches on a small subset of names.

However, I did not find a perfect match.

There was a single name in the city directory, whose name was a nearly perfect match on Z13, using both his nickname, and his given name.  I did research this person, and they worked for the city of Vallejo, on public infrastructure.  They played JV football for Vallejo High School.  Their obituary did not mention family members, and they passed away in Vallejo a few years ago.

I will not name them (unethical), and I do not consider them to be the Zodiac.  Everyone is innocent until proven guilty, and his name was not a perfect match on Z13, just one character off after a basic transposition. 

The only thing that would prove a Z13 solution is a DNA and/or handwriting match that is verified by an unbiased, qualified expert.  They will also need to have lived in the area during the right time (bonus points if they left around 1974).  They would need to resemble the sketch, and be within the age range of witness descriptions.

I wanted to share my work on the cipher, even if I am not presenting a solution.  I do have a copy of the city directory for those that want to do their own research.  You can send me a private message if you would like it.