First of all, I'm accusing CBI Ron, but I think that there's other possibilities.

So let me explain my new theory:

I'm not saying Bret Stiles, or Walter Mashburn or Virgil Minelli are not RJ, because lets think about some facts:

a) In season 2 finale, when the guy that we supposed to be RJ recites "The Tyger", you can clearly notice that's a young voice. Even if it's fake, try to imagine Virgil Minelly, Walter Mashburn, and Bret Stiles making that fake voice. Do you think it's one of them? I don't.. I think and I'm pretty sure that it's Brett Partridge.
Now,the thing is: We don't know for sure if the guy under the mask is RJ, or one of his puppets making the work for him. 
Also when Patrick talks to Red John in the limo, we don't know if the voice that we hear is really RJ, or only his puppet telling Patrick what red john tells him to say..
And this, and only this way, we can admit that Bret Stiles, or Walter or Virgil may be Red John. Because this way, Red John assures that nobody listens to his voice, not even his fake voice..

b) We also know that Red John haves Spanish/Mexican friends, because that guy whom Patrick takes out from prison is Mexican (talks the spanish language), and he says Red John is a friend of a friend of his. So we can assume RJ speaks the spanish language.
In season 2 finale, when Partridge comes to Patrick, we speaks spanish "que pasa dude?"....So, can Partridge be RJ, or one of his puppets, or none? We have to wait and see..

But, I think RJ is CBI Ron, (please read my 2 theorys about him)
Also CBI Ron only talks 1 time during the show and he haves a high pitched voice aswell. And he goes to the place where patrick, van pelt, cho etc are meeting in the office, and he says to Van Pelt that Olaughlin is on the phone (s03e08 I guess), and what can we suppose here? CBI Ron talked with olaughlin in the phone before he went calling Van Pelt, and we also know that Olaughlin worked for Red John...
CBI Ron also haves a wedding ring like Red John..

So I accused CBI Ron, even if I think that Brett Partridge is a strong candidate too, and Stiles, Walter and Virgil are good candidates too. But I think CBI Ron deserves more plausible theorys..


P.S.- We also know that RD is left handed (cause in Rosalind's house he drinks tea with his left hand. So PLEASE, stop making theorys about Patrick Jane being RJ and try to find something helpful like some characters in the show that are left handed.)

Sorry for the long post and thank you all for reading this.