At first I had been under the impression that the VN's chapters would be all involving this single case. So seeing 6 people die right away was a bit of a shock, and it quickly became obvious the entire case was going to be over in the single episode. And man, there was so much stuff to unravel I can barely wrap my head around it.
I had suspected the old lady Kumasawa for half of it. When Battler offhandedly mentioned the faces could have been disfigured to make it seem like it was a brutal attack, poison seemed like the obvious answer for the first six deaths. However once it got to Kanon's death, I knew it couldn't have been her, because she was incredibly obvious at that point. I began to suspect it was one of the original six, and Battler also throwing around that theory made it seem plausible.
However, how? I have no fucking clue. I truly believed this until the end, when during the tea party, it's mentioned the shed was locked from the outside - how could the killer have escaped afterwards? Battler did theorize the killer could have dressed up a different body and weren't in the shed at all, but that just doesn't make any sense to me. How could they have gotten an extra body?
And then there's the letter that appeared when they were in the room. I really have no idea about that one. At least with Eva and Hideyoshi's death, while I don't exactly know how it happened, surely there must be some way to take off a chain and put it back on when leaving the room (Kanon even noted it was strangely weak??). But the letter? I have no fucking clue.
The question of whether Beatrice existed or not, or whether magic was real, was never really worth thinking about to me... I knew Beatrice had a in-game sprite, so of course she is real. And if she's real, magic must be real. That said, the murders couldn't have been done by magic. I did toy with the idea sometimes (particularly after the last letter) but in the end, I just can't believe it was done by magic.
All together, my top suspect was Rosa. She was the person of the first six that I believed could have still been alive. She had a connection to Maria, and seemed the odd one out. Maybe she did it all to make Maria happy by bringing back Beatrice, or maybe she wanted the inheritance. I'm not sure, but she certainly seemed the most plausible person, and still is to me. I can't explain how she did the shed thing, or how she placed the letter inside the room, but I still think she did it.
--Plus, I noticed early on that the execution screen said for her "we'll be able to see her again".
I did mull over some other ideas, but I can't think of anything concrete. Maybe the burnt body with six toes was prepared well beforehand, and Kinzo was behind it all? Maybe there really was a 19th person, someone also from the orphanage? Maybe there were actually multiple murderers, all taking the name of 'Beatrice'? I even mulled over the absurd idea that Natsuhi was behind it all, what with her "headaches", and Kinzo praising her as a true Ushiromiya. Maybe she had some split personality thing, and killed herself when she found out she was the killer at the end.
Am I supposed to be able to get an answer with the clues provided? Is there actually a solution to this puzzle? I honestly don't know. Everything feels strange, like there's missing details. There's also the riddle to consider, but I just don't see how that's possible for us to solve.
Regardless, it has been great so far. That scene with Maria singing in the room. Christ.