Zodiac Unmasked is an extraordinarily-detailed, highly entertaining book. I recommend it to any person with a strong interest in true crime. If you really want to get wrapped up in the excitement of this case, this is a very good place to start.
Graysmith does a great job of fleshing out prime Zodiac suspect Arthur Leigh Allen. Allen is just too bizarre and complicated to be a fictional character. He's big and scary, athletic and powerfully-strong. Though sometimes prone to outbursts or physical acts toward others (he was known to throw acquaintances to the ground, knee to the chest before they knew what happened) he often appeared gentle and well-mannered. He had an odd assortment of friends and acquaintances and many unusual interests and hobbies. After both his parents died, he still chose to live in a creepy basement rather than the main floor of the house he inherited.
Though extremely intelligent and talented, Allen never seemed to reach his potential and ultimately ended up working in menial jobs. A diabetic who refused to alter his lifestyle (he was fond of Coors Beer), he later developed serious complications which caused him to lose his mobility and his eyesight.
But even in the earlier stages of his disease, Allen would have experienced diminished mobility, vision loss and coordination which could explain Zodiac's sudden disappearance from the scene. His extremely unpleasant experience being locked up at Atascadero would also explain his refusal to ever reveal his identity as Zodiac. He would not want to risk prison, especially with his ill health. He would deny that he was Zodiac up until his death at 58 from diabetes-related heart disease.
I thoroughly disagree with those here who say this book is poorly-written. And I strongly take issue with the idea that Graysmith's theory that Allen is Zodiac has now been "proven" wrong by DNA evidence.
No one, not even the SFPD, has ever come forward with evidence "proving" anything. The questionable "DNA fingerprint" said to be developed by SFPD DNA lab personnel in 2002 (6 years after their earlier, inconclusive testing) does not exonerate Arthur Leigh Allen. And, other than this SFPD analysis, there is no "other evidence" that would allow this case to reach a conclusion. The careful wording, "seems to clear Zodiac suspect" and "may" are used in press reports. Nothing definite there. Arthur Leigh Allen remains a viable suspect.
SFPD's story for publication is that "genetic traces" were found due to "powerful new DNA technology" and that "trace amounts of saliva" were found under a stamp. I would feel a lot better about this information if someone without a vested interest in the outcome of this thing, (in other words, not SFPD) had done the testing and had done it prior to SFPD's handling of the evidence. Anyone who has worked in law enforcement as I have for years (having come from generations of law enforcement) is aware of the enormous egos many cops have, especially when involved in a high profile case like this. From what I have seen over the years, I would not be at all surprised if lab personnel were persuaded to make "findings," or to overstate the significance of actual findings, that would result in this case pointing in a direction more favorable to SFPD, making them the solvers and discrediting someone they clearly saw as a busybody nobody paperboy horning in on their territory.
True DNA testing is an extraordinary crime-solving tool, but the human factor always has to be considered. There is no longer a pressing need to determine who Zodiac is or was, as he's not actively killing. This is now mostly about the public's curiosity, but also a battle of the egos. Sad to say, many people, cops included, don't play fair. Many SF cops supported Graysmith's work, but others, and most likely SF upper echelon law enforcement, didn't care for this situation at all for P.R. reasons.
As for people who feel Graysmith was unqualified, I say this: you have to be rather specially-talented to work as a political cartoonist for a paper like the Chronicle. It requires artistic ability, political savvy and, yes, an intelligence that may qualify him to actually be smart enough to figure a few things out. Homicide detectives, on the other hand, are rarely master detectives. A promotion to Homicide is a sought-after political perk mostly reserved for those well-connected in law enforcement. It is not awarded to the best and brightest. Homicide cops are usually cops of ordinary ability with some political clout. From the time I was a kid, I have heard over and over, "He got promoted to detective and he's on his way down to headquarters to pick up a bag of brains."
I'm not saying cops are worse than anyone else. I'm just saying they're ordinary people, and ordinary people cheat, manipulate and alter the truth all the time to further a conclusion they're more happy with.
Arthur Leigh Allen still looks good for these crimes, and until someone other than SFPD comes up with something provable and not subject to dispute, I will continue to consider this fascinating, incredibly-complicated, highly-intelligent man to be the prime suspect in the Zodiac murders. I would strongly encourage people who want to read this book to just do it and ignore the negative criticisms here. Like another writer here, I am really wondering if those who criticized the book actually read it. I would also recommend the movie, though it doesn't go into detail about Allen, it is well-done and well worth the six bucks.