Recently I read Simon Wiesenthal's book, The Sunflower: On the Possibilities and Limits of Forgiveness, and I was challenged to flesh out my understanding of forgiveness. There were aspects which I liked of the understandings of forgiveness by Wiesenthal, other characters in the book, and respondents to the question of whether he could or should have forgiven the Nazi who appeared to be repentant of his crimes against the Jews, but I wasn't entirely satisfied with the approaches offered.
Though there were basically three sides offered to the answer (the Jewish, Roman Catholic, and Protestant traditions), the responses were all quite short and I didn't think that there was much in the way of textual support--either from the Bible or the written traditions of the Jews or the Roman Catholic church. What I'm looking for is an explanation of the Roman Catholic or Protestant (and/or Jewish too) understanding of forgiveness, with references. I'm not interested in the subjective, feelings-based approach which many of the essay responses gave (in the second half of the text).
Edit: The Jewish response is usually something like: "You have no right to forgive someone for sins they have done against someone other than yourself, even if you are part of a group whom the apparently repentant sinner has sinned against (i.e. one Jew has no right to forgive someone for sins against other Jews but only for sins against himself). I think I agree with this. The Roman Catholic response (in the book) seems to be fairly similar to the Jewish one, but the generic Protestant response in this book seems to be that people should forgive anyone and everyone regardless of repentance(seemingly more for the sake of the person doing the forgiving than for the sake of the person being forgiven). I'm not trying to pin a position on Roman Catholics or Protestants--that's just the way it seemed to me from reading the book. So I'm trying to understand whether the book gave a representative view of these positions and I'm also trying to understand for myself who can be forgiven, by whom, and under what circumstances? To add more to the question (than the book did), in Roman Catholic or Protestant teaching, is it impossible to forgive someone whom God has not forgiven? Please do indicate what tradition you are responding from.