During a trial if you couldn't prove who killed the victim, everyone was executed except the 'blackened'. [Does that say something nasty? You can bet it does. He did say he tried to kill them all.]

Nanami Chiaki...she was very kind. Very gentle. Ah, I didn't mind being around her at all. In hindsight it makes sense she was the traitor. The rest of us have something...off about us. She never did. Even during the worst of it all she was very calm and collected.