The thing I don't get is how they live with it. I know people are great rationalizers, but you can't escape looking at yourself in the mirror and I know that would tug at my sense of justice and right/wrong for as long as I lived. For the rest of his life this person knows that he hurt another person, lied, hid and behaved like a coward. I couldn't live with that.
Your lack of understanding is something I hear frequently. They live with themselves because it doesn't bother them at all.