1x1 - Born to Kill?

Over a period of about twenty years Fred and Rose West abducted, tortured, raped and murdered an unknown number of girls, many of whom lay buried in the garden until the police dug them up. What motivated West to commit such terrible crimes? Was he born evil or did his upbringing make him this way? Did he do it for sexual kicks? Or, as some allege, did he supply the sacrificial victims to a black magic coven?