Of course, as is very typical of the nobility in War and Peace, Rostopchin cannot admit his own fault, but instead places the blame on someone else: the political prisoner Vereshchagin, who had nothing to do with the abandonment of Moscow. He throws Vereshchagin to the mob, thinking that he is doing good, when in fact he is not.
Both Rostopchin and the mob go through similar thought processes while this is happening. Rostopchin feels compelled to provide authority and sacrifice someone to the mob just as they feel compelled to obey him and attack Vereshchagin. Afterwards they both regret their actions, realizing that what they did is wrong. However, after regretting what he has done, Rostopchin then justifies his actions as necessary. This is another demonstration by Tolstoy of the stubbornness of the nobility. Even a mob can admit when they have done wrong, but the Count cannot.