Actually, when I went to examine the scene after all of you... followed Bigby out the door —

[ and he remembers that, because it was loud?? wolf bigby and all of his little ducklings rushing after him ]

From all of the blood that he tracked, it's impossible to tell exactly who moved or didn't move during the night. Personally, I also think that the situation is as simple as this: Kei tried to kill Bigby, and ended up killed himself.

But, we'll have to find a different way to prove it.