Oh my, how can it get even more complicated? So Kisei and Soutarou are maybe twins (and Ryouko married her cousin)? That would match Saikawa’s observation that Kisei looks pretty much like the professor in that blurry picture on the book cover.
The excursion about Soutarou’s book was pretty interesting, it seems like he was not the author after all. (That debunks my theory of Akira being the corpse in the car and Soutarou being the survivor.)
Apart from that, I don’t believe anything that our smart police detective speculated about (that Kisei was the murderer, coming from the outside and stuff).
Regarding deaths and stuff, if we summarize what we know so far, we have 3 dead/missing persons:
Kisei (arranged for his death 5 years ago, but was not registered as dead)
Soutarou (died in the car accident 12 years ago)
Akira (got in touch with his wife after he disappeared 12 years ago, and also sent the manuscript to Ryouko 8 (?) years ago)
and found two old corpses:
one was in the car that had the accident
and the other one was in the hole in the woods
Now, who is who? And where is the third person?
One of the original ideas (also of Saikawa) was that maybe Akira was in the car while Soutarou survived. This seems less and less plausible as (a) Akira got in touch with his wife via telephone after the accident, and I’m not sure whether Soutarou would be able to imitate Akira and fool her, and (b) if Soutarou survived and rewrote the book, wouldn’t he write it more in his style?
So my bet is that the person in the car is really Soutarou.
I checked the Internet™ and it told me that it takes about 4 years for a body to turn into a skeleton (including hair, fingernails and such). So it would be possible that the skeleton in the hole could be Kisei as well as Akira.
The other day I happened to look at the title of the book, and that gave me the idea that maybe the professor is the culprit after all? Because he really is the non-laughing mathematician, and I think as he sits at the central spot of the building, that might be a symbolism for his central role in this whole thing? But… how?
Another thing I could imagine would be Soutarou and Kisei switching bodies, maybe it was actually Kisei who died in the car accident, but they made it look like it was Soutarou? Not sure how much sense that makes, I haven’t thought it through thoroughly. Or maybe nobody died in the car accident? I’m not convinced that there was a body in the car. (Maybe is was confirmed already, but I don’t recall )
I still think that the book is written by Soutarou. Maybe he didn’t really die in the car accident. And I think the plot of the book will come into play later. Maybe Soutarou also wanted a 仙人 lifestyle, made his family fake his death, and go into the woods? Maybe he lived in that hole Moe fell into? And somehow died there?
Maybe the 仙人 and the boy represent other people in the family. Maybe the 仙人 is the professor, and the 少年 represents Noboru??? And instead of them living in the woods, they live in the 三ツ星館. They always talk about the building’s inside being the “outside”, etc. So maybe the forest in the story (the outside) represents the inside of the building.
I still suspect that Noboru committed the two murders. He’s the only one who would know of Ryoko being in his room, and he could have easily drugged her with some sleeping pills. His room is much closer to the statue as well, and he murdered her outside so that she wasn’t in his room anymore. Carrying her through the building was impossible. So outside it is. Maybe he simply pulled her out of the window from outside. He could have easily put the vase in his room first, make everyone notice it, and then moved the vase to Room 1 again. The reason he used the vase for the second murder is for everyone to recall the memory of seeing the vase in the room Ryoko was put in, to further cement the image that Ryoko was brought to Room 1.
Maybe the murders were actually not his idea, but he was pressured / asked by someone to do it. Just like his father Akira killed Soutarou (or Kisei??). Maybe the Suzuki family has a really big secret, related to Akira maybe? Maybe Noboru was blackmailed.
I’m still not sure if it’s really Akira’s skeleton they found.