***Note: If you have not yet read my book, this section contains spoilers.***
In the last chapter of my book, I try to draw on all the evidence I present to prove that my suspect was the Zodiac killer. It is a long and complex chapter that necessarily covers a lot of ground.
A simpler way of looking at things is to ask yourself which suspect explains the most about the known facts of the case.
My suspect explains the way Zodiac looked, since he was a dead ringer for the SFPD "Revised" wanted poster sketch. Not only that, he explains the reddish brown hair described for the killer in PH (AND his hair color matches the reddish-brown hair found behind the stamp from the Stine letter). He explains the Norse and British references in the letters. He explains the dates of the murders. He explains Zodiac's obsession with cars. He explains Zodiac's slow, measured manner of speaking. He explains the use of Monarch sized paper. (I still don't believe that it can be shown that any other suspect ever wrote even one letter on Monarch sized paper.) He explains BOTH how Zodiac was intimately familiar with PH AND also how he was present in Riverside on the weekend of the Bates murder. He explains Zodiac's familiarity with local lovers' lanes and with Napa County. He explains how Zodiac was able to manipulate the media with no apparent learning curve.
There is more. But I believe that my suspect explains more about the known facts of the case, and especially Zodiac's familiarity with PH (which is extremely problematical for many suspects with no ties to that neighborhood) than does any other suspect ever named. And that is why I believe he was the most likely person to have been the Zodiac killer.