Raze knew for a fact that the item he had taken from the organization Alter would be extremely effective in this situation. It was a masterpiece of deception; in fact, no one would be able to tell any difference at all between the disguise and the real person, apart from one's specific actions. He had seen the proof of its power before. It was how Henio had managed to follow through with the ultimate deception, fooling everyone into believing he was the Emperor himself.
Even when Henio had started to act differently or out of character, he was in such a high position at that time that no one felt they could question him anyway. That was the beauty of a perfect disguise combined with authority. Besides that history, it was solid proof that the mask could perfectly copy another individual down to the smallest pore and vocal inflection.
