Jem wrote:

If you have a copy of Zodiac Unmasked, you can read about the accident on pages 186 and 187 (and more about this guy on pages 188 and 260-261. ) Fred was driving a 1965 VW van and hit a 1972 Toyota. The model of the Toyota is not mentioned, but even if it were a truck it wouldn’t be the best vehicle to hit to insure death. A Mack truck would be a better target. On the other hand, a Mack truck would not be a good idea if you didn’t want your death to look like a suicide. So maybe suicide, but doesn’t seem likely. Especially since he didn’t die right away, but at 1:25 the next morning while on the operating table at the hospital. The crash occurred about 8:30, when he’d been driving for about half an hour. So possibly he fell asleep. An observer saw Fred’s headlights go out right before the crash, and there were only two feet of light skid marks, indicating he hadn’t tried to brake. Another possibility is that he had a seizure. His wife reported that he’d been having seizures controlled by medication. This is according to ZU.

The address where Manalli was living at the time of his death.

Traveller1st wrote:

Here’s what 6665 looks like today.

Allen and Manalli, both died on August 26 (76,92), if Allen had committed suicide would be strange, as was natural death, is one of those incredible coincidences, finally it is logical that the chance would be 1/365, but I do not know what are the mathematical probabilities of two suspected of such crimes died on the same date.
I am not saying anything, is how the message of the newspaper (zodiac and the Emperor)very strange.
Anyway, Manalli has almost everything, from what I read, to have been the Z. ..

Was anything ever determined one way or another about Manalli perhaps being involved in the Santa Rosa murders or is/was it speculation based on the supposed backpack(?) and drawings found in Manalli’s possession after he passed away?

Patinky, we do know that Manalli was questioned early on about his possible involvement with at least one of the SRHM. In this last batch of letters that Morf obtained, Fred wrote something about being questioned for the murder of one of his students. This student has to be Kim Allen because she was going to Santa Rosa Junior College at the time of her death. Jeannette Kamahele was also going to the JC but she has never been found and it seems to me that he would have been questioned about her disappearance not murder if she were the victim in question.

Manalli being questioned early on is something we were never sure of until Morf got these letters. This letter is dated January 27, 1973. I hope this is a satisfactory answer.

Here is the portion of the letter where Manalli talks about being questioned.

Thanks, Seagull.

That is certainly confirmation he was at least interesting enough for police to question. Wonder who the "vindictive" student could have been? The book titles are interesting too! His writing style is definitely cryptic.