At first I thought I'd already read this one, which confused me, but then I realized I was thinking of an earlier book by a guy who says his dad was the Black Dahlia killer. I'm pretty sure he felt his old man was Zodiac as well.
Didn't this guy claim that his dad hosted rape parties or something and that Man Ray attended them? Says his dad killed Smart because she looked like his sister.
Something like that. One Christmas, my sons gave me a book linking the BD killer to the surrealists.