How does Christian doctrine explain people like Adolf Hitler?

PLEASE no totally biased, stupid answers. You are entitled to your own opinion about religion/Hitler/Nazis/WWII, etc., but I am looking for a good/knowledgeable/objective answer. As for this question, I understand that the Bible is supposed to have "answers." Therefore, what is the logic/explanation behind the existence of a seemingly completely evil person if we are all God's creatures? I understand that free will is probably going to play a part in this answer, but I'm looking for other people's insights. Thanks much :]