Donald Fouke, Armond Pelissetti, and the three kids across the street are the main witnesses to the PH crime scene and we are familiar with their statements and descriptions. Eric Zelms died a few months after the attack but may have told his wife what he thought about the Zodiac, so we might have at least some hearsay info from him. But what ever happened to the partner of Armond Pelissetti, described by Armond as "an excellent police officer"? Did he say anything to anybody? How and when did he die?
Frank Peda died in a car crash in 1998.
What did he do all the time Armond was using evasive techniques to look for the Zodiac, and talking to the man with the dog? What was Frank Peda doing all the time? He never made any statements at all about the whole thing?
Since Graysmith was content to take Toschi’s word for everything, and Peda died before the massive surge of internet interest in the case…yeah, there’s a very good chance that nobody ever talked to him. I’ve read tons of articles on the case and never seen a quote from him.