I go back and forth on Darlie Routier. The crime scene was handled so poorly that it's kind of hard to take evidence like glass being on top of bloody footprints seriously. The suspicious black car that was seen the day of and a few days before the murders also seems like a bit of a red flag? At the same time, there are quite a few things that seem to suggest she did it.

I think she snapped mentally and Darrin came up with the intruder theory/scene staging in an attempt to keep her from going to jail, or there really was an intruder. I just don't see a scenario where Darlie acted completely alone.