Robert "Bob" Kirkland is Red John!
When he first met Patrick Jane they shook hands. And only after that episode, Lorelei told Jane that she's surprised they didn't become friends from the moment they shook hands.
Furthermore, he appears out of nowhere into the center of the RJ case, and seems to control some of the most powerful figures (Virgil Minelli).
In my opinion, he is too involved in this case, being just a recurring character.