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Leakage in the context of threat assessment is the communication to a third party of an intent to do harm to a target. Third parties are usually other people, but the means of communication vary, and include letters, diaries, journals, blogs, videos on the internet, emails, voice mails, and other social media forms of transmission. Leakage is a type of warning behavior that typically infers a preoccupation with the target, and may signal the research, planning, and implementation of an attack. Nomothetic data suggest that leakage occurs in a majority of cases of attacks on and assassinations of public figures, adult mass murders, adolescent mass murders, and school or campus shootings: very low-frequency, but catastrophic acts of intended and targeted violence. Idiographic or case data illustrate the various permutations of leakage. We discuss the operational importance of the concept, place it in the context of other warning behaviors, emphasize the need for further research, and outline risk management strategies for the mitigation of such acts of violence in both law enforcement and clinical mental health settings., (Copyright © 2011 John Wiley & Sons, Ltd.)

Controversy exists in the literature and society regarding what motivates serial sexual killers to commit their crimes. Hypotheses range from the seeking of sexual gratification to the achievement of power and control to the expression of anger. The authors provide theoretical, empirical, evolutionary, and physiological support for the argument that serial sexual murderers above all commit their crimes in pursuit of sadistic pleasure. The seeking of power and control over victims is believed to serve the two secondary purposes of heightening sexual arousal and ensuring victim presence for the crime. Anger is not considered a key component of these offenders' motivation due to its inhibitory physiological effect on sexual functioning. On the contrary, criminal investigations into serial sexual killings consistently reveal erotically charged crimes, with sexual motivation expressed either overtly or symbolically. Although anger may be correlated with serial sexual homicide offenders, as it is with criminal offenders in general, it is not causative. The authors further believe serial sexual murderers should be considered sex offenders. A significant proportion of them appear to have paraphilic disorders within the spectrum of sexual sadism. "sexual sadism, homicidal type" is proposed as a diagnostic subtype of sexual sadism applicable to many of these offenders, and a suggested modification of DSM criteria is presented.

The violent criminals defined in this article are a small, exceptionally dangerous group of offenders designated by the authors as "lethal predators." They have a history of sexual predation, have killed at least once, and are mentally abnormal but legally sane. They are highly likely to keep killing as long as they are free. Laws permitting civil commitment of dangerous and mentally abnormal sexual predators after they have completed criminal prison sentences have been upheld by the U.S. Supreme Court. Such laws can provide a legal means of keeping these highly dangerous killers confined so they cannot kill again.