I'm working on a new story idea about a young female teacher who is abducted with one of her students. The kidnapper is a very volatile man who has done the abduction as much for revenge as for the money. My villain is not extraordinarily bright, however. His rage overpowers his intellect. He will be acting alone in this endeavor. I am trying to come up with some sort of motivator for the crime to take place. I've considered this mostly uneducated hothead may have been fired from a job at a business that the child's father owns. It feels a bit cliche to me though. Though it is only the back story to the actual tale I still would prefer something truly convincing. The villain is capable of killing (and does kill the character of his girlfriend in the midst of the story).
You could always go the route of the antagonist having been wronged by people resembling your protagonists, be it physically or similar personalities. Some people tend to perpetrate crimes against people who are similar in some way to people that have wronged them. ETA: Though, you'd need a fresh spin on the wrong done to the antagonist because this could be a tad trite.
Sexual obsession / believing hes in love with her ? Child just happens to be in the wrong place at the wrong time
Sounds like the motivator is money? As for the revenge part, develop your characters backtory's and try to overlap them.