True, but my first idea when I read it made me chuckle. Imagine Kyoko knowing and slightly feeling that she was practically sitting on the murders lap (Him being in the chair), but didn't want to say anything since she was handcuffed to it and couldn't run away if he grabbed her, and also to teach Yui a lesson and let her figure it out. (Hopefully before he catches on first and gets her.)

Although I figure one of the detectives would be able to see the cut in the chair big enough for a man to fit in.