In the July 31st trio of letters, the Zodiac threatens to do the following if his cipher is not published on the front page of their papers:
"1st of Aug 69, I will go on a kill rampage Fry. night. I will cruse around all weekend killing lone people in the night then move on to kill again, until I end up with a dozen people over the weekend."

If we strike out the August letter as an unplanned one, due to being asked for more proofs, the trio of July letters would have been the only ones sent before the Stine attack. We can assume that he had a plan to follow on his threat if he had been completely ignored. His threat sounds of low credibility, but what if the cab attack was that threat being realized, in some capacity, but didn’t go as planned?

The attack is very unusual compared to the previous ones: Unlike LH, BRS, and LB, it is not done against couples in relatively secluded locations, and no call is made like the BRS and LB ones. It is the murder of a cab driver, right in San Francisco, which could have been seen as a random robbery if he hadn’t claimed the attack in a letter post-marked two days latter claiming it, and the attack takes place where there could have been many witnesses, and there were. I made a post about the sequence of events yesterday, but even that doesn’t bring it close enough to Occam’s razor. The killing of Stine, at that location, is just too weird, too risky, it looks unplanned.

What if he was planning to steal a cab, and go around pretending to be a cab driver for an evening, picking up people and bringing them to a murder spot? It may sound far fetched in terms of execution, but if his murder spot was expected to be somewhere in the Presidio wooded area/park, he could have sought to pick people in locations around it that allowed him to justify driving through there, bringing his victims where he wanted before executing them in whatever manner he had planned. The first one to bring to that location would be the cab itself, and hence its driver. But it didn’t go as planned.

As they approach Washington and Maple Street he tells Stine to change destination and head for the park instead of, but Stine refuses, potentially feeling suspicious of this sudden change for such a secluded location. The attacker not wanting to end his plan decides to threaten him with his gun, he asks him for his cab ID (I just found out it had also been stolen) and his wallet, but Stine is confrontational and refuses because he feels driving to the park is a death sentence, he stands his ground in this populated area hoping the attacker relents and flees. The attacker’s plans are screwed, he can’t let Stine go to the police and report him, so he shoots him and cancels his plans. He rips off the rear of his shirt, where there is less blood, to wipe off evidence he hadn’t planned on leaving on the cab at that moment, and walks away to get back to his own car parked somewhere in the park.