I don’t believe that the fatso who dubbed himself "the zodiac" killed Cheri Jo Bates nor that he was even in Riverside while it all happened, despite what Sherwood Morill had estimated. I could be wrong, but that’s my hunch.

Now, for the canonical murders and attacks – they all seem to be motivated by anger, rage towards women and jealousy over couples’ happiness and existence; all of these were mixed with hatred towards the Police authorities for some reason.

Simple math will give us the following scenarios: "zodiac" was a lonely middle aged single man who most likely was a bullied nerd while growing up, his relationship with a woman went to shit and he was accused by her for either stalking her &/ domestic violence and abusing her while they dated, he was arrested for a while and developed a lust for revenge at those who dismantled him. When he got out his ex-girlfriend already left the Bay Area and moved elsewhere, as far as she could from him.
So what else was left for him to do? work, trying to forget her and the mess she had got him into, but that wasn’t strong enough to clear his mind, he wanted the Police and others to feel his wrath, so he bought guns and practiced on animals, that didn’t stopped his egomaniacal desires to berate and embarrass the Police, so in the cold Friday night of December 20th, 1968 while he was off work for the weekend, he went on a manhunt to satisfy his need to take down happy couples and "stick it up to those fuckers who were having a good time", David Faraday and Betty-Lou Jensen were in the wrong place at the worst time.

The manhunt was postponed because he felt the Police may get him soon enough, but when it didn’t happen, he decided to strike back at July 4th, 1969 – almost 7 months since Lake Herman Road – this time only walking off with 50% of "accomplishment". If he would have known Darlene Ferrin, I guess he’d be shooting her in the head and not Michael Megaue.

Lake Berryessa (on the first day of the Jewish Holiday of Sukkot on the Saturday evening of the 27th of September, 1969) is a crime I honestly doubt was committed by the original zodiac, but for the sake of the discussion here I’ll pretend it was allegedly the same fatso and not a copycat who took his shit to the next level – it was committed to expend his reign of terror on a place he may have visited before with his ex-girlfriend who devastated him or back as a child with his family.

Paul Stine’s murder was committed just to prove to the media he could kill a man, nothing more than to silence them journalists and his ego.
After almost getting caught on that Saturday night (October 11th, 1969) and getting seen by both residents and Police officers he probably decided to quit killing since he couldn’t risk getting upperhanded (was a sloppy murderer/criminal as the fingerprints and footprints from Berryesssa tells us) and moved to threatening letters writing filled will lies and falsehoods to keep his "reputation" and terror alive.