Played it too straight, could have been done differently
Knowing right off the bat that Todd was innocent and Terry was the original killer, as well as the killer for the rest of the movie made this movie pretty lame.
When mom visits Todd, keep the part about him saying he doesn't think he was the killer. Maybe cast some doubt, but he's crazy so the audience isn't going to believe him. Show him escaping, and then keep the killer hidden throughout the movie. Show his face, sure, but the clothes would give it away. Audience is probably still going to think it's all Todd. Revealing at the end that Terry was actually the killer from the beginning would have been surprising twist.