Suppose you knew of a person that would commit a heinous act. This act would be so heinous as to cement the person's place in the historical halls of villainy amongst the likes of Hitler, Vladimir Dracula, and Pol Pot. You are the only person with enough evidence to convince you of this persons villainy. You are also certain that this person is serious about their intentions, yet also sure that they have committed no illegal acts thus far, and are unlikely to leave any evidence that would tie them to their grand act of heinousness. Basically, the question is: would you act to prevent someone from committing a second holocaust, if doing so would likely lead to your own vilification? Why and why not? Would it matter how heinous an act was to be committed? Would it matter if you would be lauded or disgraced for acting against said person?