Robert Kirkland is RJ. Why? First I would like to say why Patrick isn't. Simply, because Lorelei said "the moment you two shook hands". She knew both of them and she knew he is someone else.
For the very same reason, it has to be someone who shook his hand with Jane.
Kirkland did it. Kirkland also was the one who said "thank you" on the end of the episode showed us Patrick's beggining in the CBI.
And after the very last episode: Kirkland is a murderer, a one who have done this before and murdered because he was afraid to be identified. As who? As Red John, of course!
How is Brett Styles getting into the picture? I would speculate he might even be related to Kirkland. His father, maybe. This is the reason why he knew about what RJ is about to do but didn't handed him to CBI.