The most interesting theory, in my opinion, was proposed in Mike Kelleher's book
This is the Zodiac Speaking
: that Zodiac suffered from dissociative identity disorder, and that the personality which committed the murders eventually was overpowered by a more normal personality. In that case, it could be entirely possible that the murderer has/had no conscious memory of his crimes.
But in the final analysis, of course, we just don't know.

The fact that he just stopped without getting caught makes Zodiac somewhat mysterious, indeed. But I don't think there is any mysterious logic behind the stopping. Most likely he just got older and wiser and lost his appetite for killing. Well, he probably didn't loose the appetite completely, but being afraid of getting caught, he thought it's better to stop. Also, it's quite likely that he regrets what he's done but is too afraid to give himself up. He probably contributes a lot to charity to compensate for his past sins.

The usual reasons . He's dead , he's committed or imprisioned or he's moved a started killing elsewhere . Zodiac loved the press so I assume they got close to him and he backed off only to be arrested for something unrelated .

I'm sure it's been discussed. Especially since when BTK started communicating again Tom Voight the owner of zodiackiller.com started a website called catchBTK.com because of the similarities to Zodiac.

Has anyone considered that maybe the reason he stopped is that the Zodiac could be the same guy behind another set of murders that took place within the same or similar time frame, only set in a different state. There is one other serial killer who had been active during that time frame with a similar M.O., but was operating in a different state and has since been incarcerated: the BTK killer.

You know it's people like you that can kill a good theory. Yes Ross Sullivan or whoever it is you're obsessed woth seems like an interesting suspect. But the way you constantly post about him as if he's already guilty make people ignore anything you say.

The reason he stopped was because he was first placed in a hospital and when released he was morbidly obese. He could no longer physically do the things he use to. Then he died in 1977.

Anything is possible. But his taunting continued for a few years and he never gave proofs of his killings.

well we don't know he stopped, what if the murders didn't get coverage somehow? or where in some other place?

Because the letter writing continued at least a year or 2 after the killings stopped. Don't know the actual date but the letter with the cab drivers shirt sent to Avery obviously was written by Zodiac. I k ow the movie shows Avery opening the letter but in reality Avery was informed about it and never actually touched it.

How can you know he stopped while he was still alive?

Clearly you didn't read the post. The video documentary I'm referring to came out 10 years after he started. He's dead now for sure but I'm talking about why he stopped while he's alive.

He's obviously dead.

This message has been deleted.

Regardless of what Jack says, I too think the 1978 letter a fraud. Most documentaries say the last letter was 1974.
Even the 2005 Zodiac movie was originally titles In Control of All Things ans then scrapped it.
But notice if for sure the 1978 letter was fraud, he slipped using Zodiac in the last few letters. He wrote a citizen and Red Phantom

Instead of not saying his name, say it and what proof is there he could be the Zodiac killer.

You seem to have ALL the evidence on ROSS SULLIVAN. You really ought to get that to Michael Morford, admin at ZodiacKillerSite(.com), because he's having trouble placing Ross in Vallejo for any year! The Sullivan angle ain't looking so sharp these days Paul_Averly? duckking2001? come out, come out wherever you are and take a last bow!

The 78 letter was a fraud. He was in a mental hospital from 1970 to 1973 and then in a home from 1974 to 1977. He died in 1977. That's why he stopped.

Yes, the fact he just "stopped" is interesting, because he wasn't caught ofcourse. The last letter of the Zodiac was in 1978.
"Dear Editor This is the Zodiac speaking I am back with you. Tell herb caen I am here, I have always been here. That city pig toschi is good ' but I am smarter and better he will get tired then leave me alone.I am waiting for a good movie about me. who will play me. I am now in control of all things."
Notice its not about any murders, or a murder he is going to commit sooner or later. It looks like he just wanted to get attention again. For sure he was/is an lonely person.

Sentenced to a mental hospital and then died.