The divided personality theory holds that serial killers have a good side that often maintains the public appearance of an upstanding citizen and a dark side that is ultimately compelled to act out the killer’s murderous fantasies. In order to escape from painful memories and experiences, these people often resort to fantasy, and their personalities become divided between their fantasy self and the face they show to the real world. Not only do their dark fantasies become sexually violent, but they turn to their fantasies with increasing frequency. When a situation similar to the fantasy arises in real life, the person may automatically act out the fantasy without consciously deciding to kill. Although the killer may experience some remorse, the excitement and satisfaction experienced by the dark side may compel him to murder again and again. An understanding of the psychological processes regarding splitting and compartmentalization will aid in the detection process. If the process is not recognized and corrected, it continues unabated. References