Well, i can't say right now who Red John is. But i agree with some of the theories I have seen on this site; Episode 1-7 in season 6 will show that all the 7 suspects can be Red John, and I'm pretty sure, that we will know his identity in episode 8.
My guess on who he is.. Many. Mayby all 7, and one of them is the "leader". If I had to put all my money on one of them right now, then it would be Betram. But no one can say for sure who it is right now.
I do have a theory about Kirkland to be Red John. His interest in Red John and his break into Janes room can be a false interest to make him look innocent as being Red John. That would be a great trick, right?
I also think that too many believe in every word that Rosalind said about Red Johns look etc. If she revealed too much about him, then I'm pretty sure she would have been killed.
