I think Bret Stiles is Red John, or very close to him.
He is very interested in Patrick Jane's feelings and acts towards him, keeps talking about them.
But the main thing is, we know Red John's associates are people that were hurt before. Lorelei's sister was killed by Red John, RJ got close to her using her weakness and loss. He shows them that he can help, gets close and earns their trust. As a matter of fact, RJ first creates that weakness to make a person suffer, then gets close.
I believe that Craig O'Laughlin's being killed by Grace Ven Pelt was a setup. RJ sent O'Laughlin to kill Hightower, but how could he make sure that O'Laughlin wouldn't be successful and he gets killed?
Remember that in the mall, when Patrick Jane took Gale Bertram, he mentioned about rope during the speech, and Patrick Jane figured out that the real suspect would be O'Laughlin. It was all a matter of timing. Patrick is a smart person, as we all know. RJ knew that when he heard the word rope, he would figure out that the associate was O'Laughlin. He called Lisbon, and they killed him. Perfect timing. Remember? "There are no coincidences."
To strengthen this theory, also look at this aspect. Patrick Jane gave everyone different room numbers, so that they would know the associate. But he never thought of suspecting 2 associates. What if not only one, but two or more people were associates? Then both would give the information to Red John, and RJ would know that it was a trap. He indeed knew, because both O'Laughlin and Bertram told the info about Hightower to Red John. And he made a plan, the assassin would go to top room first, sit on bed and wait for the team to move. What kind of an assassin goes to a room to actually jump to the room below, but sits on the bed? None. It should be an in-out operation, very quick.
In the end, what is the gain? Bertram is not a suspect anymore. ( But he is an associate ). RJ sacrificed O'Laughlin, and made Grace Ven Pelt very vulnerable. The plan was that Patrick would call Lisbon, and Lisbon would kill him. But things got wrong and Grace Ven Pelt herself had to kill her lover, making herself way more weaker in the end. Way better outcome.
Remember in 4th season, Bret Stiles was trying to get closer to Ven Pelt when he was arrested for murder. First steps of the baby. We don't see personal lives of CBI members, so who knows if Bret Stiles become closer to Ven Pelt or not? Stiles was showing too much effort in trying to persuade Ven Pelt. She didn't buy it in the episode, but we don't know what happened later.
The whole act is like playing chess. RJ freed Bertram of suspicion, sacrificed O'Laughlin to win Ven Pelt in the end, as she is inside the team. Everything went according to plan.
Remember, "There are no coincidences."
