Maybe they were embarrassed by having spoken to the Zodiac and letting him go, in spite of the fact that they were, at that time, looking for a black man which, obviously the Zodiac was no.
Not sure why you find the Stine murder so suspicious. In my mind, that and the Shepard/Hartnell attack are the most convincing, although I don't doubt the other two accepted attacks either.
Some of the other other crimes attributed to Zodiac, although not officially, like Bates and Lass, are far more problematic to me, especially Lass which I find an almost amazing stretch.
Did you happen to watch the recent documentary series that ran on the History channel? If not, you might want to look it up, not that I buy everything they were selling, but it was interesting.
The suspected murders outside the "canonical five" that there's a strong chance Zodiac killed, IMO:
Robert George Domingos & Linda Faye Edwards, June 4, 1963, Santa Barbara
Johnny Ray Swindle & Joyce Ann Swindle, February 5, 1964, San Diego
Enedine Molina Martinez & Fermin Rodriguez, June 8, 1967, Alameda County
John Franklin Hood & Sandra Garcia, February 21, 1970, East Beach, Santa Barbara
Nancy Marie Bennallack, October 25, 1970, Sacramento
The couples murders have strong similarities to Lake Herman Road.
Meanwhile, Tom Voigt has mentioned three currently unreleased letters believed to be genuine sent by Zodiac to "Sacramento entities" which strongly indicate that the Zodiac Killer was who killed Nancy Marie Bennallack on October 25, 1970.
I believe that Zodiac wrote the Bates letters and mailed the Pines card, but had nothing to do with either case.
I believe that Officer Granville "Bud" Kelley was the actual killer of Cheri Jo Bates. A few years ago, he was convicted of child molestation. He also took home Bates's diary as "evidence" and
never returned it. Almost as if there was something in there he wanted kept secret. Never before or since had he taken home evidence. This is the only time he did such. Meanwhile, I don't think Zodiac wrote the desktop poem or the Patricia Hautz letter. There was an actual person named Mary Patricia Hautz, who went by her middle name. She went to the same high school as Cheri Jo Bates and had a habit of writing letters to the editor.
Donna Lass, meanwhile, was likely killed by the security guard, Oscar Victor Johansson. He was considered the prime suspect by police.
Kathleen Johns's abductor likely was a guy who kinda looked like Zodiac but wasn't him. Literally nothing in the letter is something not stated in the news articles.