A Motif

A certain time-traveler is sent back in time to assassinate Hitler. He decides the easiest way will be to go back to when Hitler was a baby in the cradle. No bodyguards, no fuss. When he arrives back at his own time, after fulfilling his mission, he is immediately put on trial for killing an innocent child. He tries to explain the evil that Hitler represented, etc... but the entire history of the world has been altered by his act, including his own orders. He himself does not understand what he has done, since his memory of learning of Hitler's evil in school seems like a bad dream. After all, he has never learned of Hitler, because Hitler was no longer a historical figure.