I thought this was an unfair call considering 'An American Crime' was adapted from the true crime story, and I personally found it more effective as a horror/thriller with it's realistic tone and attempt at authenticity versus the sensationalism of the Jack Ketchum story.

I'd never heard of the other you mention. I found Jack Ketchum's to be quite disturbing. Maybe I'll try to find the other based on the true events.

I saw both, but Girl Next Door left me utterly devastated while American Crime had pacing issues. American Crime started out so slow. I'm aware it's far more accurate (I read the entire case history online) but whether a movie is effective doesn't necessarily rely on the accuracy of the story. In fact, it more often than not relies on how the story is told. And Girl Next Door was told pretty effectively.

Girl Next Door was a brutal film to watch.