I am not sure Zodiac was born in this country, there are a lot-- lot-- of spelling errors, and I think some (perhaps even many) are intentional, ambiguous and arguably clever, but I don't think all those errors are intentional. So I tend to think he's English Second Language because with the exception of these errors, he seems very erudite. Again, jmo, if he was born in US, he's first generation American. And he's just very, very dramatic, think he's in the arts, if he's not ESL, he may be in some very "niche" track or industry when it comes to profession like music, where he's proficient in reading (and perhaps writing/composing) sheets of music/notes, but not so much otherwise. I believe him on disguises. He left survivors, if he had no disguise, I think he'd have been more careful. There was that sick medieval executioner outfit. He can sew, nobody did that for him. I've wondered if he wasn't working with a theatre troupe in the area. That card he sent, the one with the pen, it's a Jesters card, Jesters by American Greetings. His whole sick act is like a dark , cruel jester. I wonder if he wasn't aware of the airplane cement (as I look it up, this is model airplane glue?) perhaps through construction of props or perhaps even through putting together more elaborate costumes. This becomes even more alarming because he'd then be highly skilled with stage makeup and wardrobe and could craft extremely elaborate disguises for himself.
On the night Paul Stine the cabbie was murdered, they were probably preparing for opening night at Presentation Theater at University of San Francisco for Mikado. That was the very next weekend, we know Mikado's in his letters. Stine's cab was hailed in the theater district about a 12 min drive from Presentation Theatre. They were then headed to a location about four minutes from Presentation Theater. I believe Zodiac may have been at that theater earlier that day and was returning to a location near that area when he murdered Stine.
Backing up for a moment to the prior August, Zodiac sent a flurry of letters that spanned from July 31 to August 4, 1969. Auditions were advertised for the upcoming Mikado production just mentioned here on August 6. So Zodiac's correspondence ceased right around the time auditions were called for the performance, and resumed shortly before opening night after he murdered Stine. Moreover, one message was sent by Zodiac after he murdered Stine, I believe, (October 13) and more messages do not start again until November 8, which is closing night for the Mikado production previously mentioned.
I believe he murdered Cheri because of the "time for you to die" comment. It is in keeping with his sick, twisted jester persona. But it's not just the comment, it's the watch. He left that watch behind. I don't think it offered any real clue to LE, I think he left it there on purpose to dovetail with his comment about the time. It was not set to the time she died. Only Zodiac, jmo, knows why it's set to the time it is, and it may have been random. For all we know, that watch could have been related to a prior victim.
Someone on one of the Zodiac threads mentioned they thought his name might be Ken, and I have wondered on this, too. Does anyone else on here suspect Zodiac may be Dutch, of Dutch extraction? Maybe Belgian? The reason I'm wondering relates to that "Ken" point.