After seeing Where the Wild Things Are (2009), Dan Wells called Billy O'Brien and said he loved the kid who played the lead, that by the time the project got off the ground, he'd be old enough, and that his loneliness and anger were perfect for John. O'Brien agreed to look into it, but before he could, one of the producers e-mailed O'Brien saying he had a guy who'd be great for that serial killer thing he was working on. It was the same person, Max Records.
The shots of Crowley exercising are from Christopher Lloyd's actual routine. His daily workouts were noted by Director Billy O'Brien, and he thought the robotic, absent movement was so eerie, he had to get Robbie Ryan to film it. The footage would later be considered an iconic moment in the film.
The author of the novel, Dan Wells, has a brief cameo as a police officer near the closing of the film.
Based on the young adult novel series, beginning with the book of the same name. No sequels are in production (due, in part, to the independent nature of the movie), but the series has six books in total.
Dan Wells liked the concept of Crowley killing a neighbor so he could dance with his wife so much, he joked he was upset he hadn't written it.