It's bad to judge other people based on their sins.
Mark and Bill are talking when Mark admits that he has killed someone in the past.
Bill wants to respond to Mark's admission.
Bill tells Mark that we all make mistakes and that he's sure there was a reason why Mark acted the way he did but that it's all over now.
Bill tells Mark that he is a horrible human being for taking someone's life and hopes he never sees Mark again.
Mark feel supported by his friend and thanks Bill for being kind.
Mark is embarrassed by being called out and begins to cry and relive all the awful feelings from the murder incident.