The worst one for me was the Clutter family in Kansas (In Cold Blood). I think I saw the movie at too young an age, and the horror of a family just going about their daily business, leading a quiet happy life....and then hell showed up at their front door. I've never spent a night alone in a single family house with stairs, and I'm sure this is why.
The other one that chilled me was Jessica Lunsford. She was assaulted several times in a trailer with family members aware what was going on. Then she was buried alive with her favorite stuffed animal, and there were holes in the bag where she tried to break out.