The bizarre quirks of mass, serial, and multiple murderers and rapists can aid in their capture. In profiling, the psychologist uses a knowledge of a number of psychological dynamics that can provide clues to the criminal's identity, motivation, or mode of operation. These dynamics include repression, denial, undoing, restitution, regression, reaction formation, projection, rationalization, identification, turning against oneself, and acting-out. Differences between psychopaths (who lack a developed super ego and are very planned and organized in committing their crimes) and psychopaths (who are disorganized and impulsive) also can provide investigative aids. In one case involving the consecutive murder and mutilation of a series of male and female, unrelated victims, two profilers, working independently, were able to provide a description of the murderer that included his probable age, living circumstances, educational and criminal career, and mental state. Armed with this information, police were able to conduct a canvas of the area and apprehend the offender within several hours. 14 references.