I'm shocked by differences between some awesome theories of you guys ( which i think they are even better than the show itself ) and some awful theories ( with all due respect ) of some others . 

In season 5 episode 16, Red John kills Lorelei. In episode 22 it is revealed by the CD that Red John knows the 7 suspects in Jane's list even before Lorelei was killed, since Lorelei reads the list. But Bob Kirkland broke into Jane's office only in episode 19 since he does not know Jane's list previously. So Bob is not Red John.
In season 3 final episode, there were 5 people suspected as Red John accomplice including Bertram and O'Laughlin. In the Trap Jane sets, the assassin climbs down to Bertram's room by Fire stairs and is about to climb down to O'Laughlin's room through a rope. Why not directly climb down the fire escape to O'Laughlin's room? Because Bertram was Red John and O'Laughlin was his accomplice, each were given a different room number, he wanted to check both rooms. Also, in Red Queen, Bertram quotes a poem from William Blake. Red John also quotes William Blake's "Tyger Tyger".
For Sure- Bob Kirkland is not Red John
Probably- Bertram is Red John

It is a known fact that criminals such as serial killers tend to return to the crime scene. As you recall that was the case for Panzer who was pretending to help out. So if Heller still wants to be authentic in his serial killer profiling, Partridge is indeed the prime suspect to the viewers since he is always there for Red John's crime scenes.
However, since Heller has already given us a taste of a typical serial killer with Panzer, I would suspect anyone else just from a story line perspective to make it more interesting. Of course Heller also said we will be disappointed when we discover who Red John is so in that case Partridge it is.

However, some of the others on the list could have been at the crime scenes but we just not see them except for Kirkland who was there for Lorelei.
Many of you have already dismissed Kirkland for XYZ reasons because he did not kill Lennon the typical Red John's way, he did not shook hand with PJ at the right time or he did not enter PJ research scene at the right time. 
If RJ is that clever, wouldn't he make sure that he has alibis during all these times. "cannot be me I only found out then... cannot be me, I did not have contact with Lorelei during that time" 

If Heller is using the serial killer profiling of the 'returning to the crime scene' and let us investigate the clues those  two are my main suspects. 

I know he is not on the list, I`m not an idiot. If RED JOHN REALLY IS ON THE 7 SUSPECTS LIST, this is not a theory, but just an interesting fact that came to my mind.
You know how all RJ`s accomplices always say that is a charming person who can play with people`s minds. Well, Mashburn even got Teresa Lisbon to sleep with him. I mean, we know that she has a thing for Jane, so it is really difficult to make her sleep with you all of a sudden.
He always gets what he want. I think we all think at Red John as an ugly creepy person, but clues and his accomplices`s statements prove that he could be, actually, even more charming than Jane is.
I say it again, I`m not accusing W. Mashburn of being Red John, but, in my opinion, he is the most charming person (except Jane, of course) of the show. He could make any women fall from him, any man feel "small and intimidated" by his power and charisma, and he could also make kids love him. He is smart, rich and funny. Nothing like Red John. This is why he could be, from this perspective, the most obvious suspect.
Of course, he also has a thing for red sweaters. Even his employees wear red shirts. But this may be just a coincidence. Anyway, I`m sure that Mashburn is not just another character in the show.