Stopping in for some way after the rest of the book club speculations as I read this. I’ve just finished chapter 7
I am currently really bewildered/kind of frustrated at some of the really bad decisions that Moe is making. Like, she keeps on making plans to meet individually with people who she knows are very closely related with a murder investigation/could well be the murderer without telling anyone else who she is meeting/what time/who she is with. Then this chapter she doesn’t tell the police that she was with Shinozaki (there is a bit of her thinking about whether she should and then almost doing so but I feel like she should have said something straight away).
My theory up until this chapter was that Hiroshi and Sugitou were behind the murders as they were kind of just on the edge of everything but not suspicious enough to seem like a red herring. Buuut I guess that’s not correct. My current theory is that it’s either a) minoru is the murderer but the real mystery is more about the motive. Like maybe the serial murders is to divert attention away from a plan between hiroshi and minoru to kill sugitou for….some reason 
b) it was minoru’s creepy friend who Moe met at the bar, she was killed closer to 7pm and there was some kind of programming of the machines in the experiment room to make it seem like she was still alive at 7.30pm (and so giving creepy friend an alibi of meeting Moe) c) wild card - it is Kaneko, the other student that has been mentioned a few times. Getting some odd vibes from him.