From "Criminal Minds: The Perfect Storm (#2.3)"
Dominant one is the mastermind. That's not to say that the submissive partner is in any way pure or innocent in this exchange.
If their criminal desire wasn't present, their partnership wouldn't work.
The offenders share a common delusion. It's one that you and I would never accept, but it's this bond that justifies their actions.
Detective Robert Portillo
So we're looking for two sick minds who complete each other.
Dr. Spencer Reid
It's kind of like the perfect storm. Once these deviant personalities collide, they're deadly and unstoppable.