Ok now that Bruno Heller has said that Jane definitely is not RJ, and he is definitely one of the seven suspects, it has become a bit easier. http://insidetv.ew.com/2013/05/06/mentalist-finale-season-6-red-john-list/
Gale Bertram is eliminated immediately if Rosalind Harker's words "He is just under 6 ft tall and has short straight hair" are to be believed. I feel RJ will be a character who has appeared in more than 1 or 2 episodes, it makes more sense to allow the viewer to create his/her own perception about a recurring character, and then smash those perceptions. So that eliminates the Sheriff and Reede.
Could it be Brett Stiles? Maybe. The murder on one of Visualise's farms is an important clue regarding the age of Red John, and it is said the smiley was painted by a kid, barely out of his teens - so RJ would be under 50 years, which rules out Brett.
Ray Haffner was thrust into our suspicion-list in "The Red Barn" (S05E13) when he revealed he was a Visualise member, he is the right age, and he avoided Lisbon's question about being on the farm at that time. But his voice is very different from that of RJ, and one of the posts here pointed out he wasn't the right height as well. Nor does he have short straight hair. He's out too.
That leaves us with Bob Kirkland and Brett Patridge. I have a feeling Bob is not Red John, but is somehow a crucial character to the plot. There are several hints that suggest he could be the man, such as his asking to be kept updated on the CBI's investigation in "Red Dawn", his presence when Lorelei's body is discovered, his murdering of Jason Lennon and his subsequent stealth mission to get all of Jane's research. But that video of Lorelei in the season finale last week changes the game completely - it means RJ knew about Jane's suspects BEFORE Kirkland raided his room, which suggests Kirkland is not RJ, but is obsessed with him for some other reason.
Therefore by process of elimination, Brett Partridge seems to be our man - but I have to add, it's a disappointment. While he seems to love the atmosphere of crime scenes, he also has the right voice, he is the right age, he has access to the CBI because he works there, but as a character, he seems too small and insignificant. Red John knows a happy memory of Jane's, and also knows his seven suspects, and that points to a seriously resourceful and brilliant villain. Jane treats Partridge with disdain all the time, and he has had very little screen time too. But he IS a recurring character, and maybe the clue for us in the sixth season will be to see which of these seven characters are subtly being focused on.
There is however one possibility that could bring Kirkland back on top of the suspect list - what if Lorelei's murder was actually staged? Jane doesn't really examine the body, he just walks away after a few seconds. What if the video with Lorelei was shot AFTER Kirkland raided Jane's room and assembled his own copy of Jane's board? That and the fact Jason Lennon was murdered by Kirkland would make it pretty damn conclusive.
But if the writers have faked one clue, it casts a doubt on other clues, such as RJ's height and hair, which would bring Bertram back into the game. Also, regarding the age of RJ - could he have merely adopted the smiley face which was drawn by some random kid on the barn? Even if he had murdered the two guys, he could've looked at the smiley face and got the idea of marking his killings that way. By this reckoning Brett Stiles comes into play as well.
I would love to see that happen, so that we could have a rethink on who Red John is, and clues from the sixth season will prove to be decisive. But for the moment, I'm convinced that it will be Partridge, and that for me, is a disappointment.
