Kirkland. He has a weird, high voice like Red John and oddly, if you watch closely his mannerisms are quit similar to Patrick's, especially his hands.  What made me believe he is Red John was Red Dawn, the 5th episode in season 5, the 100th episode of The Mentalist. This was a "special" episode where they showed how Patrick came to be a consultant for the CBI. At the end of the show Alexa Shultz, the Director of the FBI calls Minelli and tells him she has heard about the new consultant they have hired and tells him he was in a mental institution. She then asks him to keep her informed on the Red John case so she has information for her boss should he ask for it. She is in a limousine when she makes this call and when she hangs up she looks at the man across from her, who happens to be Kirkland, and says,"done." I think Shultz is the mole in the FBI feeding Red John information. So even though Kirkland has not been visible to us the viewer throughout many seasons, he was there from the beginning. There was one other instance that caught my attention.... Red Sails in the Sunset, episode 8, season 5. Patrick pretends he has been kidnapped by Lorelei and has to wreck himself into a tree to convince everybody that was what occurred. When Lisbon finds him Kirkland is with her and speaks into his radio Patrick asks who that is, as if the voice was somewhat familiar. I also think Kirkland implanted himself into this particular investigation because he does not want Lorelei out of prison. If he did he would have helped her escape. However, Patrick helped her escape and now he has a loose end that needs tied up.....because she should have come running to him as soon as she escaped. If he still had control over her she would have. That is my theory........