I think if I had reason to believe that my father or brother was the Craigslist Ripper or Zodiac I'd want as few people as humanly possible, outside of law enforcement, to know about it. Bona fide relatives of convicted serial killers aren't usually found holding press conferences and pimping their tacit connections to murder and murderers. Same goes for the relatives of the victims. Generally speaking, human nature seems to impart an inclination to distance one's self from such things, to move forward and heal, etc. I mean, there's Steve Hodel, and the like, but generally people seem to want to keep such connections quiet.
The status of "best selling" book says nothing what-so-ever about the veracity or literary merits of said book; it just means that a lot of people bought it. The reality is that anything titled ZODIAC SOLVED, JACK THE RIPPER SOLVED, JFK ASSASSINATION SOLVED, or SON OF SAM COOKING TIPS, will naturally be apt to sell because of people's inherent interest in these subjects. For instance, there was guy who came out with a "best selling" book last year which claimed that there was a DNA match between Jack the Ripper suspect Aaron Kosminski and a shawl purporting to have been found on the body of one of his victims. The initial scientist claimed that he found a rare genetic mutation that matched both Kosminski's descendants and the shawl, but on further investigation it was discovered that he had made an error in nomenclature and had found, in reality, a rather common mutation that matched the genetic material on the shawl to about 99% of the European population. It's still a best selling book, but it's central premise has now been rendered scientifically invalid, so there's that.
A DNA evidence link between victim and perpetrator is pretty hard to beat, unless the defense attorney can raise doubts about the chain of evidence, and/or the practices of the testing lab. It has the power, almost on it's own, to convict or exonerate.
That all being said, I completely agree that if there is a conclusive DNA link between this particular "suspect" and the Zodiac I'd be reading about it in the New York Times, or on CNN, and not on a internet forum, or in someone's book. I'm quite certain the law enforcement agencies who have spent a generation or two trying to divine the identity of Z would be all too glad to issue a press release to that effect if this were the case.
In the absence of such a press release, I can only reasonably conclude that there is no such conclusive DNA link, and that the investigation continues.
Just my $.02.