Heller stated in an interview that not even the actor who plays Red John knew it was him until the script was released, let alone all the other members of the cast. This is so they didn't act different to how they normally would or let it get in the way. So even if there are images that show RJ's figure, or where we catch a glimpse of him, it could be any of them. Or even a different actor completely.

MY THEORY

Firstly I saw some theories saying the corrupt law enforcement organisation, Tyger Tyger are trying to hunt patrick. No, its possibly wrong. The Tyger Tyger is attempting to hunt Red john. They uses Patrick Jane as a lead to find the identity of red john. Almost 1/3 of the clues given on mentalist are false. Bruno Heller stated that there are quite a number of mislead-ed clues. The Tyger Tyger organisation basically has a hidden motives. We still can't find clues of its origin and whatsoever. Secondly, Visualize must be another organisation who is funding Red John for his resources. That explains how he got so many minions and owns a car etc... So basically there are 2 organisations here and there is obviously a mole in Patrick Jane group. At least one mole. My bet is Lisbon. She probably got blackmailed or worst, threatened.  Lastly the three main suspects that most of us would think is probably KIRKLAND, BRETT PATRIDGE, RAYMOND HAFFNER. The three most obvious suspects.

They say it wouldn't be patridge cause its too obvious and bla bla bla. Come on guys if its patridge also, wouldn't it still surprise everyone? How can such an inoncent guy like him, who have no involvement of killings , a retard and no backgrounds being shown become red john. If he is red john, he sure is a great actor. I would be curious of his background if hes red john.

Ray Haffner? This guy is becoming more exposed in season 6. He also getting worried, scared and angry mostly recently. This guy isn't even calm. He's shaken easily.He obviously have some connection with red john or tyger tyger.  But the personality described fits him well and he is probably quite a marksman. He could be red john himself but i will not be that surprised though cause i don't there's much of a thrill after we know that he did not kill lisbon in episode 1...

Kirkland at the other hand leads us to mysterious motive. The way he talks and do things is like red john. A natural psychopath. He is very calm and obviously do things secretly. But it will be really a confusing one if its the twin theory. Still curiosity lingers and i think his identity of red john will be a surprised one...

Lastly, unknown x, someone who have not appeared in season 6 until the 'red john' episode. This can really be disappointing or even 10x more exciting if the culprit chosen is really unexpected.

If I were casting a young Xander Berkeley, I'd cast Nick Nordella - the likeness is crazy. But in the promo for Great Red Dragon, Patrick says, "he's one of them.". One of who? Doesn't make sense he wouldn't know if he's narrowed it down to the three.. And what is the bigger lie? Can it really just be the police conspiracy? And what house do they have surrounded? Kinda looks like Napa. Only a few more weeks...who is Red John????

Okay. In my opinion, i think just because Brett Partridge is back in the Red John episode does not mean its him, i think its just a flash back and you'll also notice that Gale Bertram is there too and Agent Denyer, Oscar Coredero and Nick Nordella and Aurelio. 

This is my opinion.