I think the book you're referring to is The Girl Next Door by Jack Ketchum. That book make me sick to read, and yes, it is based on a true story. One of very few books I've ever finished with a sense of profound disgust and vowed never to return to - not because it's a bad book, on the contrary Ketchum manages to capture the wrongness of it all in compelling detail - but the subject of its story was just completely unpalatable. I was too young for that story when I read it and that was my first real taste of the sort of horrible fucked up shit that humans can do to each other. And God, there was an awful lot of horrible fucked up shit in that story. Sylvia Likens (the real life poor dead girl the book is based on) deserves to have her story told to the world but part of me wishes I didn't read it.