There we go! [Yasu is nine yet she somehow gives Sonic a Big Sister Approves smile. She has prodigious talent in many areas, apparently.] Once you have a theory like that, you know what to look for. Who was the victim expecting? What were their friends, their backgrounds?

You shouldn't dismiss really silly ideas out of hand, either. For example, if you can't find any way the culprit might have escaped, they could've just hidden in the room until someone else entered it and left in the chaos.