I believe that multiple people are "Red John". All working together and taking an element of him to work on eg one surveys Jane, one controls the police force(s), one does the killing etc. This possibility was displayed in episode two during the scene in Bertrams office with himself, sheriff McAlister and Reed smith where Reed said to Bertram he was meant to be keeping an eye on Janes progress with the case.
I also still think (forgive me, I can't remember the episode, the one with the guy who worked for RJ, got out of prison, and ended up dead with a dead lady in a bathtub) the blood writing in the bathtub was going to say "Red John is Many"
