Truth be told, Rin, has anyone in the castle really gotten together an effective punishment system? You're guaranteed a measure of leniency. If you killed him, you could blame the people in the Dead Zone. Not only would it obfuscate the true killer, but it would also give people a reason to move against the hostiles. You could also blame the castle; I had a hand in murdering multiple people over the course of my stay, and not a word was said.