The magistrate has all this disbelief for all of the inhumanity that Joll has been showing ever since he arrived, so he wants to believe that in order for Joll to walk this earth without remorse that he is somehow able to "clean" himself of all of the cruelty. By showing the inhumanity of Joll and the men that follow him, we are able to see the humanity in the magistrate. For him it is impossible not to feel empathy for the prisoners and even more so being that brutal; especially, not without having a ritual that would help him be a clean man.