
Shortly after responding officers arrived at the Blue Rock Springs parking lot they had a description of the perpetrator and the vehicle he was driving, given to them by a badly injured but "coherent" Michael Mageau. The Zodiac Killer must have known that there was a significant probability these details would be broadcast to all units in the immediacy after the crime was discovered. Despite his braggadocious nature claiming a "double murder" over the phone to Nancy Slover at 12:40am, he must have known that Michael Mageau was very much alive when he left the parking lot 38 minutes earlier. He even admitted as much in his August 4th 1969 letter, stating "The window was rolled down all ready. The boy was origionaly sitting in the front seat when I began fireing. When I fired the first shot at his head, he leaped backwards at the same time, thus spoiling my aim. He ended up on the back seat then the floor in back thashing out very violently with his legs; that's how I shot him in the knee".

The August 4th 1969 letter was carefully crafted to give police the impression he was still driving his vehicle. The Zodiac Killer stated "When I hung the phone up the damn X@ thing began to ring & that drew his attention to me + my car". The addition of "my car" appears completely superfluous to this section of text, so was probably placed there to drive home the notion of him still being in his vehicle at the payphone, when in fact "drive home" is exactly what he did after leaving Blue Rock Springs.

He stated "The man who told police that my car was brown was a negro about 40-45 rather shabbly dressed. I was in this phone booth having some fun with the Vallejo cop when he was walking by". If the police had not spoken to a "negro male" on July 5th 1969, then this would have been fairly obvious to them, and would have hurt Zodiac's previous claims. It is now clear that this "negro male" was not an invention by the Zodiac Killer to alibi his car being present at the payphone, it was a detailed description of a "negro male" offered by the writer of the letter, so that when police cross-checked with the officer who responded to the payphone that morning, the description given by the Zodiac Killer matched with that of the officer. He gave a detailed description of the black man's age and clothing to "prove" he was near the payphone when the officer responded from Blue Rock Springs.
The section of police report below describes a responding officer (RO) traveling from the crime scene to the payphone after being informed that the perpetrator had called police (12:40am). If the responding officer took 9 minutes to arrive at the payphone, a traced call at approximately 12:41am, would mean that the Zodiac Killer observed the interaction between the "negro male" and officer at about 12:50am. Long after he had finished talking to police dispatcher, Nancy Slover. The location of the payphone was the only logical place the Zodiac Killer could have seen police talking to anyone. Had the responding officer's superiors confirmed his interaction with "a negro about 40-45, rather shabbly dressed" at the payphone, it would have added credence to Zosiac's claims that the black man also saw his "brown car". A vehicle that was likely never at the payphone, because the Zodiac Killer had gone home after the attack, separated himself from his vehicle, changed his clothes, ditched his weapon, and walked back to the payphone to deliver his sinister message to Nancy Slover. If he was unlikely to be at the payphone at 12:40am with his vehicle, then he most certainly wouldn't have been at the payphone in his vehicle at 12:50am or beyond. Fifty minutes after a shooting that he couldn't have been certain both victims were dead.

If the "negro male" had passed him by at approximately 12:40am when he made the phone call to Nancy Slover, then it makes sense that this was the same man who spoke with police a short time later. Had police verified this by talking to the responding officer who arrived at the payphone, it would explain why the Zodiac Killer added his car into the equation. Because without a car - calling police from a payphone 38 minutes after the double shooting, from a location only 9 minutes from the crime scene, would have focused investigators attention to residences in close proximity to that payphone. Watching the police at the payphone at least 9 minutes after he finished the call with Nancy Slover, would have raised even more eyebrows. That is why the Zodiac Killer may have made special emphasis of his car and its color on August 4th 1969.