usually "forgiveness" is a meaningless term in today's psychologically oriented world, meaning that you forgive someone who never harmed you so that you can think yourself a good person, or when a person who had nothing to do with the actual bad deed says he apologizes for that deed (e.g. that his ancestors might have done to your ancestors, or maybe not). Again, the real meaning is to make someone feel superior to one's ancestors, not to actually repent for something they themselves have done.
Ah, but real forgiveness is hard, but necessary to a person so that they can release their inner bitterness and learn to freely love themselves and others.
Plough magazine has an article about a woman forgiving Dr Mengele and those who killed her family.
Go read it and ponder the story.
update: The magazine also has an essay on Bonhoeffer