There's an interesting pattern in 4 of the 7 suspect's names, likely symbolic:  the name "BRET" can be found in the names of: Brett Partridge and Bret Stiles; AND [Gale] BERTRAM and ROBERT [Kirkland] also rearrange to "Bret" as well.  Bret is a place name, meaning from "Breton" or "Brittany" -- a part of France that used to be a part of England; Breton meaning "a lesser or little Britain," as opposed to "Great Britain."  Breton is where the King Arthur legends purportedly took place.  Interestingly, STILES means ASCENDING [as in fame or high place]; the name BERTRAM means KNIGHT; PARTRIDGE means NOBLE; and KIRKLAND means CHURCH LAND.  KNIGHT, NOBLE, CHURCH LAND -- the writers are telling us something here.  And I think that the use of the word "BRET" in each name denotes their involvement in the "round table" of Visualize --- with each man and their individual name representing their specific role.  STILES is at the TOP of the "Visualize Church"; and I think that Bertram, Kirkland and Partridge are a few of his most trusted "NOBLE" "KNIGHTS" who protect the "CHURCH LAND" and carry out his vision.  Visualize is a highly organized, corporate stylized CULT -- and if you look at the history of cults, which I did via Google, PARTICULARLY of California or "CULTIFORNIA," it's creepily commonplace.  SO, while I think BRET STILES, the leader of the cult Visualize, is the mastermind behind Red John  --- I do not think RED JOHN is one specific person.  I think Red John is a creation comprised of many:  Bertram, Kirkland and Partridge, each fulfilling a role in the "kingdom."  We already know Kirkland is a corrupt follower of RJ but he hasn't the leverage or charisma to be in charge of so many people at once.  Bertram has more power, being in a great position to let many "pawns" into the CBI though I hate to think Bertram is a bad guy -- but somebody is hiring all these people who end up on the inside, though Bertram just doesn't seem to have the drive to be "recognized" in the way that someone like RJ does.  Also, I think it's safe to say "ghoul" Partridge is the one who actually does the gruesome killings [enjoying investigating his own handiwork, as others have mentioned].  Initially, I felt Partridge was RJ, because I felt he was the killer but it just wasn't enough that ONLY Partridge was RJ as he is just not that charismatic enough to have power over others.  Partridge is more of a follower.  Kirkland is a follower and Bertram is a follower.  The only leader is Stiles:  Stiles controls all of these people  and has created RED JOHN to be thought of as one individual person, a "serial killer" on the loose as a RED HERRING, to throw PJ and the CBI team off the trail of Visualize.  PJ has been looking for his one true nemesis, but I think he's going to learn that this enemy is in the faces of many.