The motivational forces that underlie the behavior of serial sexual killers can be indirectly assessed through their psychiatric diagnoses. Most serial sexual killers have some degree of sexual sadism. Krafft-Ebing defined sadism as "the experience of sexually pleasurable sensations, including orgasm, produced by acts of cruelty. It may also consist of an innate desire to humiliate, hurt, wound, or even destroy others in order thereby to create sexual pleasure in one's self." According to DSM-IV-TR, a diagnosis of sexual sadism requires that over a period of at least 6 months, recurrent, intense sexually arousing fantasies, sexual urges, or behavior that involve acts in which the psychological or physical suffering, including humiliation, of the victim is sexually exciting to the person. Twelve brief case examples presented in this paper all feature the killer's feelings of sexual pleasure, rather than anger, as the dominant experience in killing their victims. The exercise of power and control over the victim to the extent of taking away their lives is part of the sexual arousal as well as a practical necessity for obtaining sexual arousal. In challenging the reasoning of those who attribute the actions of serial sexual murderers to "anger" or "rage," the authors argue that the aggressive acts involved in controlling their victims do not stem from anger or rage but rather from the sexual arousal derived from being able to make the victim be a prop for fulfilling sadistic sexual needs. The paper concludes with a discussion of how to conduct valid research interviews with serial sexual murderers in a way that exposes their motivation for their crimes. 88 references