I have no idea what motivates Prado either. So many possibilities bouncing around in my head, and it may be a combination of all of them. Early on he seemed to be familiar with the stalking aspect of being a killer. He also recognized Dexter's dark side, but initially he came off as someone who manipulated the justice system but hadn't crossed over to murder. I just hope Dexter rubs a little salt into the wound before he sticks his knife in Prado by telling him it wasn't Freebo who killed his brother.