The narratives focus on 544 cases of serial murders, involving about 750 individual murderers and an estimated 5,336 to 6,368 victims. Seventy-four percent of the murderers were from the United States, where 85 percent were male, 8 percent were female, and the sex was undetermined in the cases in which the offender was still at large. In addition, 82 percent of American serial killers were white, 15 percent were black, and 2.5 percent were Hispanic. Eighty- seven percent operated alone, while 10 percent committed their crimes in pairs or groups. Some committed their crimes in specific geographic areas, while others traveled widely. Motives were often psychological, with strong sado-sexual overtones and evidence of compulsive behavior. Six percent of the cases involved greed. Since 1969, 8 percent of the cases involved practitioners of Satanism, while another 5 percent involved members of the medical profession.