The granting of forgiveness, especially in circumstances like this, is such a powerful and moving thing – such an essentially human thing – it's small wonder that virtually all religions have annexed it, as they have love, spirituality and the notion of truth itself, as a way to bind human beings to themselves. Some have made redemption, the seeking of or granting of forgiveness, the very core of their belief and practice. It should hardly need saying, but then again perhaps it does, that forgiveness and redemption are no more the creations or possessions of any religion than soul music is an invention of Adele.
True, religious traditions have produced some of the most beautiful meditations on forgiveness, and served as a way of reminding societies of its importance, but it does not belong to them. I'm no evolutionary expert, and I'm pretty sure that we have yet to turn up a forgiveness fossil, but it seems obvious to me that the human art of forgiveness developed as a necessary skill to ensure group coherence, in the light of the (also very human) tendency to do horrible things to other people in furtherance of your own interests. Human societies needed rules, and rules mean establishing what is beyond the pale, and forgiveness is the mechanism by which those who have gone beyond the pale may be brought back.