At the risk of giving you blood pressure, DB, Fox's view is mostly the opposite to this, and there's a boring amount of explanation on another thread that you probably don't need to read.
Zodiac - a 2 man job?
I don't believe the Berryessa attack was made by the same person as the other three attacks in the true Zodiac canon. To me, it's not an evolution or a devolution, it's a completely different psychology. Killers, they change their MO, not their motivation. So for me, The Santa Rosa Hitchhikers, that's a travelling/roaming lust-driven serial killer, quite possibly from another state, not the rage-fuelled punishment-motivation of the Bates murder or the Berryessa attack, nor are they the business-like,
indifferent Zodiac of Lake Herman and Blue Rock Springs, very much the type that the FBI describes as a "Comfort Killer", killing to maintain a lifestyle, protect a reputation, an identity, a secret, or so forth.
People have wondered why the murders apparently stopped. Possibly the answer is simply that the Zodiac didn't need to kill anyone else. But of course he may just have moved up the US-50 to Tahoe and beyond...
Hope I haven't hospitalised anyone, it's just a point of view.