Whoever killed her mailed in a confession and described details no one else would know. Then mailed multiple cards that were very similar to Zodiac cards.

"Details no one else would know"? That’s a pretty bold claim.

What exactly were these details available only to the killer that were not in this letter?

Indeed, if anything, it seems the letter writer far more stuff wrong (like only two stabs wounds) than right.

I think whoever killed her did type out the confession letter. I absolutely do. Btw, did the papers mention Cheri being kicked in the head? Because she was, and the letter writer did in fact mention that. That would be some random right on guesswork for the letter to have been a ruse or fraud. When the writer mentions the knife breaking, it more than likely did, especially if it hit a bone. Nearly decapitating someone shows how hard and brutal these stabs were. The very top of the knife could indeed have broken. Doesn’t mean a big piece has to break.

I have to also wonder if the watch wasn’t planted there. Very possible! I’m in a metro area that’s busy, and it’s pretty easy to find things laying around such as bracelets, an earring, old watches and so on. The watch isn’t too convincing that it belonged to the killer. It could have, but not necessarily. The watch could have been there already. Who knows? A young couple could have been making out or anything and it fell off.
I’m just not convinced it belonged to the killer….