Many details of the crime were printed in the newspapers, including an "awful scream between 10:15 pm and 10:45 pm and then a loud sound like an old car starting up". The author of the letter uses this scream in his letter, stating "she let out a scream once and I kicked her in the head," along with the presence of his vehicle: "I told her that my car was down the street and that I would give her a lift home". However, if he knew she had exited the library to find her car disabled, then his story doesn't work from the standpoint of a 10:15 pm to 10:45 pm attack, as the library closed at 9:00 pm. Besides, he stated he followed her out of the library after about 2 minutes, and we know she left prior to 6:30 pm. Why is the author (if the killer) trying to give the impression that Cheri Jo Bates never left the campus that evening, when clearly her movements were unknown for approximately 4 hours?
The author blatantly disregards the time of 10:15 pm and 10:45 pm in his continuous timeline, but certainly makes use of the scream and vehicle, to give us the impression he had killed Cheri Jo Bates moments after she exited the library. Does he weave his vehicle into the story to convince us he had to travel a reasonable distance to arrive near the alleyway, and therefore lives a reasonable distance away, when in actual fact he lived within walking distance of the Riverside campus. If the author of the 'Confession' letter was the Zodiac Killer, he may have used this tactic nearly three years later, when using his vehicle as evidence he didn't live close to the payphone at Springs and Tuolumne after the attack at Blue Rock Springs.
If Cheri Jo Bates had left the library annex voluntarily before 6:30 pm and hooked up with somebody who lived nearby - who then escorted her back to her vehicle at around 10:30 pm, then the disabling of her vehicle could have taken place while she was present during an altercation. This would explain both windows rolled down, the right door being possibly ajar and the keys present in the ignition. A murder at approximately 10:30 pm with little passing traffic is an altogether more likely scenario, particularly when we consider the screams heard by eyewitnesses.
The author and killer would have been unaware at the point of writing, of a female student and man present in the alleyway with no body, and was desperate to shift the timeline 4 hours earlier, thereby ruling out any possibility of Cheri Jo Bates having ever left the campus to a nearby residence with somebody she knew. The use of his vehicle in the letter was the window dressing, to paint a completely different picture to the one that really happened that night - that Cheri Jo Bates was escorted from the campus on foot at around 6:30 pm by somebody she trusted. Somebody that would eventually betray that trust a mere 4 hours later.