(I ended up editing this a ton while writing it because writing down my thoughts made me come up with a ton of new possibilities 
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And now the characters also arrived at the same hypothesis I did a few chapters ago, even if they also dismissed it before the chapter even was over(for obvious reasons).
I do think the robot was involved though, not just in a nearly as complicated way as Saikawa guessed at first(I kind of wonder why he didn’t assume as many things as possible were done by Magata Shiki before dying though, like for instance her putting on the wedding dress in advance would have been way easier than the robot somehow doing it).
You could really simplify his hypothesis a ton by 1. Modifying it to have Magata Shiki herself do the things she could have before dying and 2. just having the one surviving robot assemble and disassemble a single murder robot and then throw it away instead of making it some weird murder robot disassembly loop. If you do that I only think you need a second culprit for the roof murder to make it all work out(unless I missed something again or there’s something we don’t know yet)
I’ve also been trying to think about who could have done it, and if Magata Shiki was involved the ones that seem like they would have the most obvious means of committing the murder would probably be:
Yamane(he’s in charge of most of the stuff so it would be super easy for him to lie and hide his tracks if he had done something), but he was also with Moe so it’s probably not him
Magata Shiki’s sister(it seems possible she could have had contact with her sister in some way at some point, and we already know she was obviously near the helicopter so if it’s true nobody went up there she would be the likeliest culprit purely due to having been on the roof without going there from within the research facility, and she could just have lied about her missing bag. There doesn’t seem to be any real motive or even hints at a motive for her to do it though, and I’m not sure how she could have done it, but I also can’t think of any other possible culprit that doesn’t cause contradictionsif it can be assumed all the records and stuff that have been mentioned are 100% true)
the doctor(If I recall correctly there was a mention of his wife having visited Magata Shiki at one point so there was at least previous contact that could have been used to set up a plan, and most of the information the characters have about the how the murder could have been committed comes from him. I don’t remember if he was at the facility from the start though and there was also no record of him going up to the roof).
By the process of elimination the sister seems like they would be the likeliest culprit(it’s the only way I can figure out to solve how the murder on the roof happened with no records of anyone going up there: If the evidence doesn’t work if someone went to the roof, then nobody went up there at all and the murder was somehow committed by somebody who we already know was there). Now that I think about it, if the murder on Magata Shiki was done by disassembled robot you could conceivably have both be done by the same culprit, aside from the dress because then that makes no sense.
In my version of events it could hypothetically have played out like:
Magata Shiki’s sister sends in a disassembled murder robot along with the tv guys or something that Shiki ordered. The Michiru robot assembles the murder robot when it’s time for the murder and then disassembles it to throw it into the trash. At the same time the stuff with the computers is also done. A bit later Miki arrives on the rooftop and somehow sets the rooftop murder in motion right after the helicopter lands, and that’s basically all that actually happened.
However, there are still a few things that bug me with my reasoning outlined above(assuming it’s correct which there obviously is no guarantee for):
- how would the sister have gotten access to the computers? Did she just use the robot for that too? I guess it’s at least not entirely implausible, but I’m also not entirely convinced.
- what exact means did she use to commit the rooftop murder?(another robot that threw itself off the rooftop? That seems a bit ridiculous though, especially considering we have no hints of anything like that at all. Just stab him right before she steps out of the helicopter? Seems like the others would have noticed that though)
- Why would she even do all of that in the first place? It’s unnecessarily complicated and she has seemingly zero reasons for why she randomly would commit the murders fifteen years after the only thing I could think of that could be a potential motive.
- Just something the time stuff made me think of, but why does Magata Shiki look so much younger than her younger sister? Is it just one of those weird character traits you’re supposed to accept? (Alright, I doubt this has anything to do with the mystery but it’s still felt weird ever since she was first described since it seems weird she would look 15+ years younger than she’s supposed to be and than how old her sister looks considering she’d basically look like a young teenager at that point which is pretty far from an adult). Actually… if I’m allowed some really crazy speculation, almost nobody knows what Magata Shiki looks like and she only ever appeared on screens and not in person, so what if she somehow swapped places with her sister and what we’re seeing is actually that Magata Shiki murdered Miki instead of the other way around? That would still raise the questions of both how and why though. I’d be happy if this somehow was relevant though because I really like when things that just seem like standard character tropes you’re supposed to take at face value turn out to actually be foreshadowing for something more(for instance I read another book where a character described as tired all the time no matter how much they slept actually turned out to actually have problems with depression). Now that I think about it, it makes no sense for the people at the research facility to not have noticed something like that though.
Finally, Moe asking Saikawa to wait with telling her at the end felt a bit weird considering there could be a murderer around and it seems like solving the mystery as fast as possible would be in almost everyone’s best interest and take way higher priority than trying to solve the mystery on your own. No one in this book really comes across as having much of a sense of self-preservation considering how much people have been to places alone/with only one other person(I think someone mentioned that in a previous thread as well).
From how I read that situation it seemed like there was some kind of romantic subtext, but their age gap is making me a bit uncomfortable, so I don’t quite like the thought of shipping them or anything like that 
Also a bit scared of y’all judging me if I did 
I’m still only halfway through, and you’re reeeeeallly cranking up my suspense to 150% !!
), and on top of it, this is a series…)