I first heard the rumor via le, but also believe I read about the crashed van in Greysmith's 2nd Zodiac book. Currently lost among my bookshelves.
"Zodiac" by Robert Graysmith
"This Is the Zodiac Speaking" by Michael D. Kelleher
"Zodiac Unmasked" by Robert Graysmith
Includes in passing LE found a crashed van;
Driver killed in crash, who had evidence in the van that might have made him a main suspect, but decided to leave the dead man's reputation intact and concentrate on Leigh Allen instead.
mine are hardcover but:
"Zodiac Unmasked" Paperback: 512 pages
Publisher: Berkley (March 4, 2003)
ISBN-10: 0425189430, ISBN-13: 978-0425189436

[link to www.zodiackiller.com]

You might take note that a police composite looked like those in the unibomber case, and made Ted Kaczynski a suspect.
[link to www.serialkillerdatabase.net]
The zodiac is just another example of citizens assaulted by criminals.
btw: DNA from the cryptic Zodia letters excludes Allen as a suspect.
[link to www.zodiackillerfacts.com]
>Attempts to extract DNA from the letters proved successful and Dr. Cynde Holt and others were able to develop a partial genetic profile. Members of the SFPD believed that the DNA profile belonged to the Zodiac and was valuable evidence useful in eliminating suspects.
... Arthur Leigh Allen was among those suspects excluded by DNA comparison<