It would depend on how quickly their deaths arrived... and whether or not they had any idea who their attacker was. [ie kaoru has no idea, which seems to be a theme this trial.]

If it weren't for the fact that both were in their rooms, I would think that perhaps the burned item was the passage map. That can also be hidden without the use of flame, though... But perhaps whatever it was, it was burned while the leg was being charred? It would explain why they did not get rid of it in the fireplace, at the very least.