It's a guy with different personalities but we know only at the end. It start with a couple on the side of the road and the kid push is mom and the front of a car. They go the nearest motel and they get stuck there with other persons cause it rain too much. One after one they die and at the end; only a guy that we didn't see before left and should go to jail cause he's the one with multiple personalities.

Identity (2003) (http://www.imdb.com/title/tt0309698/)