When the Zodiac Killer rang Nancy Slover at 12:40am he stated "I want to report a double murder. If you will go one mile east...... On Columbus Parkway to the public park, you will find the kids in a brown car. They were shot with a 9 mm Luger. I also killed those kids last year.... Good-bye". His phone call would have ended at approximately 12:41am The details behind this call were then relayed by Mrs Johnson PT&T operator to police at 12:47am, while we assume the trace by Betty Main on the open line was still ongoing. When the trace was effected (estimated at 12:56am in the previous article), police at Blue Rock Springs were informed of the payphone location. This is assuming a trace took 15 minutes in 1969.
When Betty Main (or another) rang back the payphone, Zodiac removed the receiver and left the scene. However, where was the negro male at this juncture? If he was hanging around the area at the time, he may have belatedly noticed the hanging receiver and heard Betty Main on the other end, resulting in him picking up the receiver and talking to her. She may have immediately asked him to provide the location of the payphone, which he did at 12:47am. This could explain how Betty Main "traced" the payphone call in only six minutes and why the Zodiac Killer stated on August 4th 1969 "The man who told police that my car was brown was a negro about 40-45 rather shabbly dressed". If the Zodiac Killer saw the negro male picking up the receiver at 12:47am and providing Betty Main the payphone location, it would mean that the Zodiac Killer still had eyes on that payphone six minutes after he unhooked the receiver.
This question hinges on how long it took to trace a payphone in 1969. If it was traced at 12:47am, yet this process took at least 15 minutes in 1969, then the negro male becomes far more important to this story, bearing in mind he was placed at the payphone by the killer himself. Did the negro male request anonymity and why Betty Main's supervisor didn't immediately allow her to give a statement to police? The supervisor freely told police that Betty Main had traced the call, so what else happened on that open line that made her reluctant to allow Betty Main to be interviewed. Was it her conversation with the negro male?
If the payphone location was traced before 12:47am (by the operator being given its phone number) and this time was only relevant to when Mrs Johnson called the police, then the responding officer from Blue Rock Springs could have been informed of the payphone location shortly after the Zodiac Killer initially hung up the phone. This would have placed a police officer at the payphone several minutes earlier (approximately 12:50am). But was the Zodiac Killer still in the area, observing the negro male converse with the officer?
THE PAYPHONE TRACE IN VALLEJO [PART ONE]