Top Suspect: Agent Ray Haffner
Obviously after the most recent episode, Red Barn, Haffner has to be among the leading suspects. The writers weren't especially subtle about it, considering the tension between Haffner and Lisbon when Lisbon found out Haffner was a Visualize member.
Then again, the guilty person is rarely who the writers want you to suspect.
I discuss my reasons for believing Haffner has to be taken very seriously as a top Red John suspect - or if not, someone very close to him - according to criteria I have for Red John. But first are my criteria (in addition to the obvious criteria established in this website's "clues"):
1) Age (45-55) - Red John Must be someone close in age to Patrick Jane, or perhaps slightly older. He cannot be too much older (ruling out Bret Stiles), because he would not be able bodied enough to fit the character we saw at the end of "Red Sky in the Morning (2-23)," or the relatively youthful hand of "Roy Tagliaferro" we saw at the end of "Red is the New Black (4-13)." Moreover an old fart wouldn't be a suitable nemesis for Jane anyway. Neither would someone younger. We know RJ has to be at least around 45 anyway to fit the timeline established in "Red Barn (5-13)."
Ray Haffner is the appropriate age.
2) Charisma/Virtù - The most difficult thing for The Mentalist writers to explain will be why a serial killer has an entire network of fervently loyal, capable, and powerful disciples? Serial killers simply do not have organizations, especially not vast, well oiled intelligence/influence operations that infiltrate numerous govt. agencies. Historically they have occasionally operated in pairs, but that's about it. A serial killer his own intelligence agency is a major stretch that must be explained.
So what is it about Red John that enables him to operate as he does and command such cult like loyalty?
Money? Red John must have at least a modestly significant independent source (serial killing doesn't pay, unless he's a hit-man for hire, but that doesn't fit), but no amount of money can command this kind of cult-like devotion.
Know what might help Red John inspire cult-like devotion? A cult. Which is why it surely surprises no one that closer and closer ties between Red John and visualize are continually revealed.
But in addition to drawing from Visualize to inspire his following, Red John must also have a sort of "virtù," as Machiavelli would call it (http://en.wikipedia.org/wiki/Virt%C3%B9). A weaselly man such as Timothy Carter could never inspire the devotion of a confident, high achieving guy like Craig O'laughlin as well as other FBI and LE agents. Nor could he be William Blake's predatory "Tyger."
Red John inspires such followers with strength, wisdom and intellectual charisma as well as a level of personal charisma. The wisdom (or perceived wisdom) requirement reinforces that his age is likely in the 45-55 range.
Ray Haffner is the appropriate age, yet still very able bodied. He is also relatively handsome and capable of considerable charisma. He is accomplished, as was established in "Little Red Book (4-02)," having started his career with the FBI Organized Crime Division using "creative surveillance techniques."
3) Law Enforcement - I am convinced Red John must almost certainly be in law enforcement. How else could he have so many loyalists in the FBI, CBI, etc.? The FBI is a very insular organization, and they don't look up to outsiders the way these guys look up to Red John.
Haffner is former FBI and with his record of success at the FBI,
4) Other Criteria:
Ray Haffner shakes hands with Patrick Jane the first time they meet in "Little Red Book (4-02)." He also then puts his hand on Jane's shoulder, a universal sign of condescension. Haffner has moved in as Jane's boss, and perhaps he has engineered this situation in hopes of recruiting & mentoring Jane much earlier than we realized (in the final episode of Season 5). There is no question Haffner wants to be Jane's friend. This not only establishes Haffner as someone who shook Jane's hand, but someone who sought to make friends (perhaps "lifelong friends") with Jane as soon as they shook hands. Haffner also fits because he is someone Jane clearly did NOT make friends with.
We know that Red John wants to see himself as a mentor figure to Jane. He would view it as perhaps his greatest achievement/victory to bring golden boy Jane into is following and convert him to his own perspectives as he has so lesser challenges in law enforcement. Haffner's efforts to do the same in "Little Red Book" make Haffner a perfect fit for Red John.
Haffner is also about the appropriate height - Roy Tagliaferro was around 5'11. Reed Diamond, the actor playing Haffner, is slightly over 6'0. And he has short hair, like Roy, as described by Rosalind Harker.
As a bonus, perhaps "Roy" is a natural alias for someone actually named "Ray." For what it's worth "Haffner" means "potter," which doesn't appear to have anything to do with "Tagliaferro" or "Cut Iron." But perhaps we will see Jane test Haffner at some point by calling him "Roy" instead of "Ray."
Also, consider the actor himself. Whoever ends up being Red John, the actor playing him surely must be capable of giving us all a satisfactory villain, the way Bradley Whitford did as Timothy Carter. Reed Diamond (Haffner) has shown he can play the straight arrow cop, as he has done in The Mentalist as well as his other work. But he would also be fully capable of playing one fantastic villain. Just look at the man's eyes.
Ray Haffner as Red John just makes too much sense. Can anyone give good reasons why it isn't Haffner? I don't think anyone else would fit the bill nearly as well.
Simon