A suspense novel about a man (who we learn at the end of the book) is a cop who breaks into a home and murders the entire family, not knowing that a college friend is visiting. She escapes being murdered by hiding under a bed. She ultimating gets caught by him, taken to his home where she finds a child being held captive in a hidden room.

http://en.wikipedia.org/wiki/Intensity_(novel)

Sounds like intensity by dean koont. He has a camper van which he takes her girlfriend in and she thinks ghat she is still alive so she hides in the van to help her and gets caught.