As an explanation of criminal behavior, "spiritualism" emphasized the conflict between absolute good and absolute evil set in a metaphysical context. People who committed crimes were thought to be possessed by evil spirits, often referred to as demons. The Classical School of criminology posited that criminality may be chosen or rejected based upon each individual's action of free will. The most significant difference between the Classical School and the subsequent Positivist School is the latter's search for empirical facts to confirm the idea that crime is determined by multiple factors. The modern search for multi-factual explanations of crime is usually attributed to Cesare Lombroso (1835-1909). The most obvious orientation displayed by positivists of the mid-19th century through the first quarter of the 20th century was their placement of crime causes primarily within individual offenders, most notably in their biological constitution and processes. This led to the practices of sterilization and psychosurgery on targeted "high risk" populations in the United States even until well into the 1970's. Policies based on theories must be recognized as being a mixture of empirically based and socially and culturally based influences.