Why He's Guilty: Caleb has always been a strong contender for "A" because of his technological savvy and general shadiness. Given the fact that he's romantically involved with Spencer, he's more tangled in this web than ever. It's definitely interesting that he's managed to stay so involved with everyone else, isn't it?
Why He's Innocent: Even after all this time, Caleb's main mission seems to be protecting Hanna, Spencer, and everyone else. It directly conflicts with the motives of this new villain.