I believe he is RJ.  During the season 1 episode 11 "Red John's Friends", Minelli took a 'vacation', and suddenly CBI gets communication from RJ?  How convenient.   Also, when Minelli left Rosalind after drinking tea, the figure of RJ looked like him.

Minelli knows how to charm older women, as he is middle aged himself.  His eyes, actually look quite evil.

Also, Bob Kirkland could be Lorelei Martin's brother, wanting to avenge her and his dead sister, since they all look hispanic.
Therefore he gave RJ's accomplice a death he could not fight off, painless but the fact that he couldn't stop him from injecting that substance must have felt great great vengeance. 

Also, BK asked: "Do you recognise my face?"  Because RJ's accomplice at the hospital knows Lorelei Martin, and her sister, but perhaps not the brother, him.

BK hates RJ.

Minelli is RJ.  He too shook hands with Patrick in a flashback episode in season 5.
Reed Smith, and the Sheriff? Oh come on, they were jus random cameo appearances.

'Minelli' is an italian surname as is Red Johns alias Tagliaferro

When Jane and the CBI go to Tiujana, Mexico in "S1 E11 Red John's friends" Minelli simultaneously has gone on holiday.

At this point Jane had resigned to Minelli.

Red John contacts the CBI team directly via computer during this holiday time. He asks "is Jane there?". 

If Red John was anyone else he would have known Jane was there.

Season 5: - "A friend in FBI" phrase of Red John is/might be fully confirmed in 5x05
Season 5: - "Shooked hands" Minelli suits that role for that quote in 5x08 said by Lorelei M.
Season 1: - Can't exactly remember which episode it was, but when the team was chatting with Red John's account via the computer, the eye vision reflected from the computer of the opposite side (which was in that case, Red John) might belong to Minelli himself, as he can easily access the CBI network
Season 1: - Minelli might have resigned in order not to make Jane suspicious about him as a Red John candidate
Season 2: - He keeps in touch with Patrick and helps him illegaly in an investigation, which can be a tactic of the writers to keep Minelli in the frame, as his role was not essential for recurring after his resignment in the end of the first season; by that, we can also say that writers intentionally shoot the episode 5x05 to keep Minelli in the game
Personal reasons: Gregory Itzin, who is a terrific actor, plays for the bad natured character more than usually in series or films, so he has the right aspect and charisma in the words of being the Red John
Personal reasons 2: In these kinds of fiction, the identity of the main antagonists turn to be someone that the audience knew from the very beginning, so Minelli is very appropriate for that role.
Roy Tagliaferro: By the measurements of body and size described by Harker, Minelli
suits to be the alter ego/alias of Red John
*He definitely has no alibis in many of the murders

The writers confirmed the narrowed-down list of Jane's, but that doesn't mean that the list is the absolute correct cage to hold all the candidates within it. Writers have every right to mislead the audience at all times, that's a well known tactic of fictionists.
His motives to be Red John is exclusive yet, that's for sure. But hence, he has many sidekicks and associates to build up such good network.
That's my best guess...

I believe its Minelli because of several things.
The first one that jumped out at me was in the flashback episode to Jane joining the CBI.  Minelli seemed very keen to have Jane on board.  And that phone conversation he had with Agent Shultz, where she said it would be good to have a friend in the FBI. Red John has said himself he has a friend in the FBI so that may be it.
The other thing is his age.  RJ has to be older than Jane given the time the murders started and when it was said he was the friend of Dumar's father. Minelli looks to be right around the right age.
RJ has found it very easy to access CBI network servers.  As the boss and former boss, Minelli could very well still have access to do things like upload the vido of Agent Darcy.
Lastly is the easy way that he left CBI. This has left him plenty of time to do the things RJ does, whether that be murders or turning new followers.

Virgil is 'Red John'

He left CBI just after De Boscos team were wiped out and he gave an unconvincing speech to the press

Also, in season one, the episode 'red Johns shoes' Virgil is shown walking up a staircase in CBI with red shoes on. - but this scene was cut from the aired show and was a deleted scene

At the time of filming season 1 the writers had no idea of how sucessful the show would become and so wouod have needed somwone from the beginning to be Red John in case the show was pulled and a swift conclusion to the mystery was needed

Virgil also gives Patrick a list of suspects, a red john list made up by red john himself

Heres the clincher... in another deleted scene from season one, patrick is talking to virgil... virgil is drinking tea... and on the bottom of his cup.... is this symbol.... :)

i was not sure before but now i am. it is clear that the producers were not gonna let us now who is the real red john among those seven suspects, so when i saw that Virgil Minelli wasnt on the list, it made me reinforce my theory. he is someone unexpected, he fits the physical conditions described, he has appeared from the beggining of the show, since season 1, and he suddenly resigned the cbi. jason lennon, who was a friend of RJ, liked to fish, and Virgil has also been seen fishing, 

Red John is VIRGIL MINELLI

Red John's Friends episode

MinelliI: Wake up, Dorothy. You're not in Kansas anymore
Jane: If I'm Dorothy, then who are you?
Minelli: It doesn't matter who I am

At the end of episode appears the famous HE IS MAR...
In "The Wizard of Oz" one of the characters is the Professor MARvel (captivating but false soothsayer).
I Think the message on the wall is an answer to the question of Jane.