My theory about the Zodiac killer
So, it's true that Arthur Leigh Allen was obsessed with Vallejo victim Darlene Ferrin. Zodiac survivor Mike Mageau picked Allen out of a lineup, but he gave two different height descriptions, and he also remembered someone having a fat face, which Allen didn't have. Also, the night of the shooting, two different vehicles pulled up to Ferrins car before the attack. The movie made it look like they were ten seconds apart, but it was actually ten minutes.
So, it's very plausible that Allen was stalking Ferrin, and discovered the bodies after the shooting. And Mageau remembered his face, which is why he picked his picture.
I'm a strong believer that Rick Marshall and Bob Vaughn were behind the murders, with Marshall doing the killings and Vaughn doing the writing.