It’s interesting to me the postmarks on the Zodiac letters are always San Francisco. Today it is not uncommon for all the mail in an area to be sent to a central processing facility for cancellation but in the late 60s individual post offices were expected to cancel as much locally collected mail as possible before the final dispatch to the processing facility. That said, if Zodiac is not from San Francisco (and I think that’s likely) then he is physically in San Francisco or its close environs to mail his letters. Assuming for a moment he was living in Vallejo or Benicia then why is he mailing his letters from San Francisco (or close by)? It would seem to imply regardless of where he lives he has to go to San Francisco with some regularity. That would mean he very likely had a car and a job. We know based on his tire tracks it isn’t a well maintained car, so his job would probably not be well paying. But he makes enough money to drive to San Francisco when (if the job were really menial) he could just as well find comparable work around Vallejo. This implies he had some marketable skill, and we know he had at least enough disposable income to purchase an array of weapons. We know also after Lake Berryessa he was heading south of the scene of the crime (stopping in Napa to make the call taunting the police). We know he has a basement, by his own accounts, so he’s not in an apartment. He’s got some mechanical/electrical experience (based on the circuit diagram for the bomb) and at Lake Berryessa he’s in a costume with a squared head like an old fashioned welder’s hat. My guess would be he lived in Vallejo and drove up to San Francisco to work at some sort of shop. Could be a welder or repairman in a shipyard. Has access at a drafting table most likely (based on the precision of the letters and symbols in the cipher and the appearance of lighting behind the paper on one). Maybe ex-Navy with access to the post exchange (for the boots) at one of the military bases in the area (which also makes him older than most people seem to think he was). All of this is conjecture and based on the supposition the killer lived near where his initial victims were killed. I don’t say any of this with certainty and don’t think my guesses are better than anyone else’s. But at the end of the day we don’t have access to physical evidence and except for the people really dedicated to sifting through a lot of information we’re all just speculating.