Papaerchase emails:
In his book Dark Dreams former FBI profiler Roy Hazelwood says that the the most likely explaination is one of socioeconomic class and cultural influences. Serial killers are typically men who engage in ritualistic sexual behavior. (Ted Bundy, John Wayne Gacy, the Green River, and BTK killers) The opportunity to develop the deviant fantasies seems to be linked to middle class and higher status. As more African Americans and hispanics move into the middle class, more serial killers from these groups are emerging. (see pp. 94-98 for this discussion). By the way, most of the information on such offenders is antidotal because they are quite rare. At one point in the 1980s the FBI thought there might be 30 operating in the USA at any given time. (not counting those in jail) That would be perhaps slightly more than one per 500,000 males.
Interestingly when it comes to ritualistic sexual offenses there are far more serial rapists out there then serial killers.