Im going to present my final theory. THIS will defined who is Red John. Im going to put ALL the suspects here:

-Jason Cooper
-Madeleine Hightower
-Vint Molinari
-Brenda Shettrick
-Craig O Laughlin
-Dean Harken
-Sam Bosco
-Dr.Linus Wagner
-Dr.Royston Daniel
-Dr. Steiner
-Luther Wainwright
-Summer Edgecombe
-Susan Darcy
-Ellis Mars
-Reede Smith
-Lorelei Martins
-Oscar Ardiles
-Wayne Rigsby
-Roselind Harken
-Thomas McAllister
-Kimball Cho
-J.J Laroche
-Kristina Frye
-Grace Van Pelt
-Ron (CBI Ron)
-Teresa Lisbon
-Virgil Minelli
-Ray Haffner
-Walter Mashburn
-Bret Stiles
-Gale Bertram
-Bob Kirkland
-Brett Patridge

WE MUST REDUCE THE LIST WHO :
-Are police offciers and Shriff / CBI Agent / FBI Agent / Security Homeland officer / Vizualize Members
And the one who are "death" eliminate them.

List:

-Jason Cooper
-Madeleine Hightower
-Vint Molinari
-Brenda Shettrick
-Summer Edgecombe
-Susan Darcy
-Reede Smith
-Oscar Ardiles
-Wayne Rigsby
-Thomas McAllister
-Kimball Cho
-J.J Laroche
-Grace Van Pelt
-Ron (CBI Ron)
-Teresa Lisbon
-Virgil Minelli
-Ray Haffner
-Bret Stiles
-Gale Bertram
-Bob Kirkland
-Brett Patridge

RED JOHN IS A MAN. SO WE HAVE TO ELIMINATE THE WOMEN HERE:

-Jason Cooper
-Vint Molinari
-Reede Smith
-Oscar Ardiles
-Wayne Rigsby
-Thomas McAllister
-Kimball Cho
-J.J Laroche
-Ron (CBI Ron)
-Virgil Minelli
-Ray Haffner
-Bret Stiles
-Gale Bertram
-Bob Kirkland
-Brett Patridge

RED JOHN HAS 30 - 55 YEARS SO WE HAVE TO ELIMINATE THE "OLD ONES" (ONLY LEAVING BERTRAM)

-Gale Bertram
-Bob Kirkland
-Brett Patridge
-Ray Haffner
-Ron (CBI Ron)
-Reede Smith
-Oscar Ardiles
-Wayne Rigsby
-Thomas McAllister
-Kimball Cho

PATRICK JANE AND RED JOHN ARENT FRIENDS SO WE HAVE TO ELIMINATE PATRICKS FRIENDS:

-Gale Bertram
-Bob Kirkland
-Brett Patridge
-Ray Haffner
-Ron (CBI Ron)
-Reede Smith
-Oscar Ardiles
-Thomas McAllister

NOW WE ARE GOING TO ELIMINATE THE SUSPECTS THAT ARENT IN THE LIST:

-Gale Bertram
-Bob Kirkland
-Brett Patridge
-Ray Haffner
-Reede Smith
-Thomas McAllister

WE KNOW THAT , IN THE MENTALIST , THE OBVIOUS SUSPECT ISNT THE MURDERER. SO KNOW ME HAVE TO ELIMINATE : BRETT PATRIDGE.

-Ray Haffner
-Reede Smith
-Thomas McAllister
-Gale Bertram
-Bob Kirkland

WE HAVE TO ELIMINATE BOB KIRKLAND , BECAUSE JASON LENNON DIDNT RECOGNIZED HIM AND REEDE SMITH , BECAUSE HE IS TOO FAT. Only leaving:

-Ray Haffner
-Thomas McAllister
-Gale Bertram

WE HAVE TO ELIMINATE THOMAS MCALLISTER. WHY? BECAUSE THE ONLY SUSPECTS THAT WERE MENTIONED BY TERESA AND PATRICK WAS GALE BERTRAM. AND RAY HAFFNER WAS THE MOST CLEARED HEARD SUSPECT (MENTIONED BY LORELEI)

-Ray Haffner
-Gale Bertram

THE ONLY ONE WHO WORKED IN VIZUALIZE IS RAY HAFFNER SO ... HE IS RED JOHN !!!

Well , Im going to discover NOW who is Red John , so this is a VERY HUGE SPOILER

1- I have seen a photo where Reede Smith , Sheriff Thomas McAllister and Gale Bertram are with PJ but this says that they arent RJ. This photo is gonna be show on S6 E2.

So , if we count that , only this suspects are RJ-
-Brett PATRIDGE
-Bret STILES
-Raymond HAFFNER
-Bob KIRKLAND

2- Lorelei told PJ that RJ wasnt his friend since they shoked hands.So Bret Stiles isnt RJ

So now the list is - 

Brett PATRIDGE
Raymond HAFFNER
Bob Kirkland

3- RJ has 30 when he started to work on Vizualize.So Brett Patridge cant be ... he also didnt work on Vizualize.

So now the list is-
Raymond HAFFNER
Bob KIRKLAND

And the only one here that fits with all thew clues is ... RAYMOND HAFFNER. HE IS RED JOHN.

After watching most of the episodes again I am convinced that out of the 7 Haffner is RJ.

The hints at survaillence and FBI connections. Trying to manipulate Cho, offering Lisbon a new job. All things that have been discussed by other posters.

For me the thing that sealed it is the handshake. Haffner is standing atop a small mound looking down at Patrick. Trying to impose power over someone perhaps.   

At the end of it I trust the writers to deliver an epic season six. I for one cannot wait.

Hi everyone.
Today I lift a secret about Ray Haffner.
I'm starting with the contacts. After that: the handshake, the money and the surprises.

First of all his contacts.
- He is a former FBI Agent so he has friends and contacts within the FBI. 
- He is a Visualize member, long enough to have been at the farm in 1988. That is the reason why          Bret Stiles knows so much about Red John. 
- He is a former CBI Supervisory Special Agent and Agent Senior and chief of the new Team when Jane was reinstated so the shook hands.
This is the reason why Wainwright truested him. And we all saw what happend. May he rest in peace.

The money. 
- He offered Lisbon a new job at a new private security agency where she would have a substantial pay raise. 
That explains the money for a Limo and the armed gorillas. 

So far, so good.
Surprise #1.
Haffner was the only one who ever quoted William Blake. Some lines of The Tyger. And you know who does it too.

Surprise #2.
Did you saw the picture of the killed woman with the name "Roy"? The sister of Loralei? Sure you did ;)
It shows the name of Red John, ROY.
But do you see the similarities between Roy and Ray? Me too.


Summary.
You see, Haffner got the right contacts, the money, shook hands with Jane, is a Visualize member and knows The Tyger.
Do you need more hints or conclusive evidence?

In the end I would like to sit back drink some tea (btw. I love tea) and wait for your comments. Thank you.

Tyger Tyger, burning bright, 
In the forests of the night; 
What immortal hand or eye, 
Dare frame thy fearful symmetry?

Hi,

First of all, I don't have any real theory that would confirm my accusation, I just hope it's him. I sort of like his character.

Furthermore if you read a crime novel (e.g Agatha Christie) you can come up with educated guesses but with The Mentalist it's different. To many suspects fit a part or all of the clues. 

I do believe that casting for Red John is trickier than we would think. Nobody can estimate in the first season precisely how long a show will go on so you always have to have character that could be RJ. If the show continues you can expand the legend and create new story lines. At least this is what I would do as a creator/executive producer and this is why we have so many possible suspects and theories.

Bret Stiles, Gale Bertram, Ray Haffner, Reede Smith, Robert Kirkland, Sheriff Thomas McAllister, Brett  Partridge - One of them IS RJ. Its been confirmed by the creator and others. 

Red John most likely has some kind of link to Visulize and is also well funded, he can pay for Limos, buying property and even a new life for Jane.

Smith and McAllister have not been in the series enough times to be the main bad guy, also Smith is fat, RJ isn't from what we've seen. If one of them was RJ it would be extremely disappointing. 

Kirkland shook hands with Jane an episode before Lorelei told Jane they shook hands, she can't have expected them to become friends in one episode ?

Partridge and Jane do not get along, Jane insults him and calls him a ghoul and he also talks about murders that were not committed by RJ as if they were, RJ hates them. 

With them eliminated i believe that RJ is one of these 3.

Brett Stiles.
Ray Haffner.
Gale Bertram.

And out of them i pick either Haffner, he has money, proven by offering Lisbon a job that had a huge pay check and he has his own agency and is an ex agent so would have loads of contacts. 

But in a way i hope i'm wrong and when RJ is revealed its a total shock !!!


Cheers

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.