/sci/ - Science & Math

I wasn't sure which board to post this one, but figured this one came the close, as forensics and forensic psychology would best fit under /sci/

Why is it that serial killers often hunt within their own ethnic group, that never made sense to me, why is it they're more often men, and finally why do so many target prostitutes, is it because they're less likely to be missed, are easy prey, or because it allows them in their mind to think of them as being less than human, so that they feel less guilt of their crimes?