Why It's Him: Caleb has always been a little too close to the drama. He's tech-savvy, which would make it easy for him to execute these grand schemes. He's nowhere to be found at the end of the Summer finale. Isn't it strange the way he and Mona behaved in the Radley Hotel? How they fixed up each other's tea? Isn't it interesting to think about how intent he is to distract Hanna from getting back to Noel Kahn when she has him in captivity? Something's not adding up.
Why It's Not: At this point, it seems like whatever "A.D." is holding onto runs deep. It's an old pain. Unless there's a part of Caleb's backstory that we haven't heard yet, we're having a hard time locking down his motive. What could possibly drive him to enmesh himself so deliberately in torturing the liars? Caleb may be shifty sometimes, but he always seems to have the girls' safety at the top of his priorities.