You don't really need to know how or why this guy came to be in the house. Actually why is pretty obvious - he's a psycho driven by control, power and sexual perversion. You can accept what he does,safe in the knowledge he will pay for his crimes in the most terrible way by the end of the film. That should be the point of a film like this, the realisation of the family of what has actually been going on, the sadistic crimes that can only be cancelled out by an even more sadistic end for the perpetrator. The film might have been acceptable if that had happened. But no, there is no point in the suffering and ultimate death of the happy parents, the boyfriend, the handyman, the murderer survives to kill again. Who on earth writes an end like that, what sort of a viewer enjoys the fact he gets away with it and indeed is seen to be lining up another set of victims? Perhaps someone who looks forward to making or watching a sequel, perhaps with the same disappointing ending, maybe a real-life serial killer who thinks that the guy is a hero? Like other recent films with similar endings, what would have been a sensible and satisfying end for most of us is sacrificed in favour of a 'clever' ending that leaves you feeling you've just been cheated out of a couple of hours of your life.
