However, social scientists have gained some knowledge about these criminals, who may number as many as 100 in the United States alone. In general they are white males, aged 25 - 34, of at least average intelligence, and often with charming personalities. Many were illegitimate and experienced abuse as children. They tend to select vulneralbe victims of some specific type who gratify their need to control people. They prefer to kill with hands-on methods such as strangulation and stabbing.
Many serial killers are impressed with police work and like to associate with the police.
Although the incidence of murder has been disproportionately higher in the South, serial killers are not likely to hail from Southern states. Over the course of their criminal careers, their murders may become less organized and more poorly planned. However, the contrary has also been observed. The visionary type feels compelled to murder because he hears voices or sees visions ordering him to kill certain kinds of people. This type is often psychotic.