A serial killer is defined as an individual who murders two or more victims over an extended period of time, ranging from days to years, with the crimes often being sexually motivated. The personal motivational models profiled include psychophysiological approaches and psychological models. The sociological approaches explained include containment theory, conflict theory, and urbanization and serial murder. Integrational models described are the motivational model developed by the Behavioral Science Unit (BSU) of the Violent Criminal Apprehension Program and the "disease" model developed by Norris. The BSU model attributes the source of the serial killer's deviance to an ineffective social environment in which the child is not provided with adequate social bonding or guidance. The individual's development could be so distorted that escalating aggressive and violent responses would emerge. Norris' disease model integrates biological factors with environmental influences. In addition to innate genetic or neurological anomalies, Norris notes a number of environmental factors, including child abuse and negative parenting. This leads to a loss of the sense of self, resulting in antisocial or asocial personality characteristics. Further damage to the individual's functioning may result from chemical imbalances induced by alcohol and drug use, prolonged malnutrition, and poisoning from environmental toxins. 61 references