Aha but that's the trick see:
! Notice.. there were already 3 people at Ishimaru's corpse when Naegi got there. 3 people.
! Monobear announces a death when three people see the corpse right? The explanation is simple, both parties got to the bodies around the same time, hence why one party thought only Ishimaru was murdered and one party thought only Yamada was murdered.
! I don't know if Celes planned that with the redirecting, or she just got lucky. But hot damn.
! mmm, I must have missed that. I was thinking that Naegi found Ishimaru all by himself, and then came back and got the other people, and brought them to see the corpse, then ran down to find Yamada's body missing, then ran back to find Ishimaru's body missing, and I though "jesus shit just stay in one room asshole" but now I get it.