Red John must have been working in Visualize farm in 1988 while in his teens or early twenties. Red John must have the physical power to hold and bind and slit them. He cannot be Bret Stiles or Gale Bertram or Sheriff McAllister, they're too old; it isn't Partridge, he's too young. There's also other reasons against them.
Gale Bertram cannot be Red John because if he was Red John then at the end of 3rd series when Jane's team informs the five suspects of Hightower's place with fake room numbers then O'Laughlin would have one number and Bertam another so they would know about the scheme and wouldn't act upon it; also Bertram needs Jane's help in playing poker and is genuinely frustrated at his loss.
Bret Stiles is miserable when he thinks that someone tries to replace him in Visualize and needs Jane's help; He cannot be our super-genius killer.
Partridge is in one occasion easy to judge a murder scene as a classic Red John and is pissed off when Jane finds out. If he was Red John he wouldn't have been so obsessed to underestimate Jane's skills in identifying a Red John scene.
And about the Sheriff (Thomas McAllister) and the FBI agent (Reede Smith): wouldn't you think it would be hard for someone in their ranks to pull off a charismatic character of a leader who is able to easily affect people like Kirkland or O'Laughlin? Certainly not; and again Reede Smith is a little younger to be our guy and a little less sophisticated, it seems.
And about Kirkland: the first time that Jane meets him and shakes his hand is one episode before Lorelei tells Jane that she wonders why they didn't become friends the moment the shook hands. This strongly implies that this hand-shaking has happened long time ago not the previous episode; after all she wouldn't expect them to become friends in one episode!
So who remains? Haffner. I have reasons against him but also for him. He's a member of Visualize so Stiles information on Red John can be justified but the fact that Jane easily gets rid of him in "Little Red Book" doesn't strengthen our suspicions. So I'm not sure but he's the most plausible suspect. If not him then it's Reede Smith. It sure sounds a little pathetic and cheap but I realize that my reasons againts him are not as strong as the other ones.
