Guilt

As both a psychological and literal thriller, "Killer" plays heavily on the theme of guilt, which each character, including the minor ones, experience to some extent. Obviously, the main issue is the guilt of the killer. As one of the killers whose motives go unexplained or that you guess at throughout the novel, some of Jason's actions can be read as stemming from guilt. For example, he befriends one of his sister's friends - the same girl to whom he gave Ali's piece of the flag years ago. Apart from the murder, however, each of the girls has her own secrets, which trouble them deeply. Spencer's is her relationship with the woman she thinks is her birth mother, and her subsequent loss of her college funds. Hanna has a partially-hidden contempt for her stepsister, though she does not feel guilty about this. She does, however, feel some guilt...