Sex Slaves: The Psychology of Mastery
Partnerships
Among the partnerships in which sexual slavery was involved, although usually for a shorter time then we've seen with lone males, are Fred and Rosemary West, Karla Holmolka and Paul Bernardo, and Judith and Alvin Neeley. Even the Countess Erszebet Bathory got her start tormenting hundreds of captive young women by teaming up with her sadistic husband.
In such incidents, two people who feel a strong attraction to each other begin to spice things up with the coercion and violence of third parties. Typically one is dominant, and that one seduces the other into acting out a specific sexual fantasy. Once a crime has been successfully committed, the dominant partner wants to repeat it. In the case of two equally dominant partners, they egg each other on, emboldened by the other's ability to participate.
David and Catherine Birnie coerced young girls into sex in Australia during the 1980s. They met as children and started their life of crime with a series of robberies. Although jail parted them, they eventually reunited in 1985. Schechter wrote in The Serial Killer File that David introduced the idea of kidnap and rape. Together they lured a young woman to their home near Perth, chaining her to a bed. David raped her numerous times as Catherine watched. When he had exhausted his desire, they took the girl to a wilderness area, strangled her, and dumped her body.
They did this three more times, with each incident growing increasingly more violent until Catherine apparently had had enough. She allowed the fifth girl to remain unbound, giving the girl a chance to escape. She led the police back to the house of depravity, and both offenders received life in prison.
While couples do get involved in such incidents, it's the lone male who tends to keep slaves around for a while.