That would mean the narration is full of lies…? I know narrator murderer is a thing but it doesn’t seem very likely to me here. But happy to be proven wrong, maybe if you look closely at the narration there aren’t that many lies I dunno.
I thought that our mannequin girl is actually the only one with a strongly visible motive, what do you think? Getting rid of the son‘s two lovers (or whatever they meant to him) and then going in and securing him for herself Also if it is true that the murderer used the small window to move from one room to the other, then she (as a woman) would be a suitable candidate - and if we believe Sasaki that his girlfriend has enough of an alibi through him, then she’s actually the only female suspect
Which is exactly why I don’t think it’s her ^^’ I dunno I have no idea who did what how so I just go with “whoever seems like an obvious suspect is probably not the murderer, and whoever seems really unlikely probably is”. We’ll see at the end of the book how well that worked x)
A detail I’m sure will be important: the older sister has short hair in her driver’s license picture, which she would have renewed a month previous.
That reminds me of how the owners son cried more for the younger sister, and how his relationship with the older sister was strained recently… Maybe they switched places for some reason? I don’t remember how their features were described, do they look very similar…?
I’ve lost track of the description of the two rooms 娯楽室 and 映写室. The latter had the younger sister with the rope, right? Moe explained how it’s possible to go from one room to the other through a small window, but only one way, not both. Which was it again?
I personally think 橋爪 papa is sus. I get the impression that he knows too much and he’s pretending like he doesn’t. And I feel like he should’ve questioned more whether the cause was suicide or not. “What do you mean, ‘murder’? It was suicide, obviously. Isn’t that evident?”
The 娯楽室 is like a home theater, and the 映写室 is a projection room. The projector in the 映写室 projects into the 娯楽室 via a small window high up on the wall between the two rooms. Normally, the window is blocked by the projector.
Edit: The next two paragraphs are the opposite of what Belerith said, so I guess one or both of us have lost track of the characters’ various theories
A person in the 映写室 could move the projector out of the way, go into the hall, enter the 娯楽室, lock the 娯楽室 door behind them, do something dastardly, go through the window into the 映写室, move the projector back, and then lock the 映写室 door as well.
The culprit couldn’t do the opposite because once you pass through the window from the 映写室 to the 娯楽室, it’s impossible to move the projector back (because it’s heavy and hard to move from the opposite side of the window).
Also if it is true that the murderer used the small window to move from one room to the other, then she (as a woman) would be a suitable candidate - and if we believe Sasaki that his girlfriend has enough of an alibi through him, then she’s actually the only female suspect 
