"Would the writing on the car door be enough to convict Zodiac had he been caught for one of the other Zodiac murders"? Asks Tahoe27. The topic then expands into all aspects, including handwriting analysis, the validity of this attack being placed under the umbrella of Zodiac murders, the specifics of the crime and the phone call from 1231 Main Street, Napa, to name but a few.
The Lake Berryessa crime, the third in the series, showed a marked deviation from the two previous attacks at Lake Herman Road and Blue Rock Springs, in that the attack displayed a flair for the dramatic, when the supposed Zodiac Killer donned a black executioner's hood and a waistline bib. However, despite his theatrical entrance, this was soon to turn deadly.
To view this thread: Zodiac Killer Net

Three young women, students of Pacific Union College had traveled to Lake Berryessa for a spot of sunbathing, parking their vehicle two miles north of the A & W Root Beer stand on Knoxville Road. After they had exited the car, a white male, driving a silver or light-blue Chevrolet 2-door sedan with California plates, pulled up to the rear of their car but remained inside his vehicle. Thirty minutes had elapsed before they noticed the same man, approximately 50 feet away, observing them sunbathing - and each time they looked at him he evaded eye contact. He was described as 28 to 40 years of age, 200 to 210 pounds in weight, 6 feet tall, styled black hair, with rounded eyes and thin lips. The young women added that he was good looking, with a muscular or stocky build, wearing dark pants and a dark pullover shirt. The composite sketch of the man drawn from the women's recollections that day is shown to the left.
The Zodiac Killer Net forum thread, started by Tahoe27 can be accessed here