I was just looking at this. Go figure!

So he says 10 in a 4/20/70 letter:
Oceanside
Domingos
Edwards
Swindle
Swindle
Walker
Bates
Faraday
Jensen
Ferrin
Shepherd
Stine

That’s the 12 most likely. So, not far off.

6/26/70 letter, he says 12, including a man in a parked car.
man in parked car, a Reddit user says a civil rights activist was shot in a parked car in Riverside around this time. So the whole cop thing might be a bad assumption.
??????

7/26/70 letter: 13
???

10/31/70 Halloween card: 14
Bennallack

3/31/71 letter: 17+
Donna Lass
????
????

I don’t think the number are all that hard to believe, actually.

If you can help me fill these out, it would be interesting.

Santa Rosa hitchhiker murders adds a maximum of seven.

There was the 13 hole postcard sent, the Halloween card (14) and the St. Patrick’s Day card with ebeoriet on it as well as the other letters such as "x" and "Y" and Oriental characters and words such as "glen", "roze", "elen", "land" written in the shape of a cross.

I’m with Jacob, the zodiac case and the Santa Rosa hitchiker murders are linked together, Eileen Hynson could possibly be added to that list

I’m with Jacob, the zodiac case and the Santa Rosa hitchiker murders are linked together, Eileen Hynson could possibly be added to that list

I wasn’t aware of the Hynson case. The fact she went missing from Lake Berryessa seems almost unreal, but serial killers do tend to strike in familiar geographic locations.