Some have wondered why God allows terrible things to happen (war, murder, rape, adultery, etc.). Quite pointedly, God prohibits such activity. He doesn't pull the trigger; he didn't tell them to plant the bomb — people do these things. God clearly teaches us how we should behave, but he then allows us to freely choose what we will do. Only if an evil thing is actually done can a person be punished for it.
Often, God does not immediately punish us for the evil we do. It is his sincere hope that we will repent and choose to follow his commandments.
Regardless of whether or not a person has remorse for their wrongdoings, we are required to forgive them. "For if ye forgive men their trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses." (Matthew 6:14-15; Matthew 18:21-22, 35; Luke 6:37)
Never forget that heavenly father's own son was cruelly murdered. He knows personally how those parents feel.