I think that it is Brett, but Frye is involved somehow. Here are a few theories:
1: Maybe, Frye and Brett used to be lovers, but now they split up, and RJ is after Jane for revenge (although this isnt likely)
2: I dont think atall that Frye is dead (sorry cotdepalbo) and getting her back will be a really big part in RJ's plan. Maybe RJ is Jane's father, as he has many reasons, although I don't see what killing Jane's wife was for. Maybe he wants Jane for himself, and that is why he has taken Frye. (And killed Jane's wife)

Also, I think that it is possible that one of the team are involved, but I really hope not!!!!

I don't really think that I like Frye-she seems strange-and maybe if she is involved, that would give her and Jane a reason to split. I hope that happens because Lisbon and Jane belong together!!!!

im pretty sure kryistina's dead now so it couldn't be her. i don't think we know red john yet. im sure he would have kept an eye on his insiders so we may have seen him but i don't think he's anyone we know that well.

it was Christina in the outfit. The voice was feminine and small in stature. She is missing but knows way too much about Red John. It would make for a great twist.

When I saw Red John on the show, I was surprised (and a little dissapointed) at the high and not-so-terrifying voice. I immediately thought of the annoying forensics guy who suddenly re-appeared in the last episode. Why else would they bring him back?

I don’t see how Red John could be Kristina. Red John was involved with the secretary that killed the other CBI unit and the people that have been involved with Red John throughout both seasons refer to "him". The forensics guy is an interesting theory because that guy fits all the info that we have. Since we see him from behind when he killed the secretary with the poison in a previous episode and again in this episode, we know Red John is slight of build (which, by the way, precludes him from being the roll tide waiter). If that was his real voice then that also fits with the forensics guy.

I think Kristina is one of Red John’s pawns. When she was confronted by Jane about going on TV, she had that serene look on her face, like she knew him so well. (Oh, I know…she’s a psychic. Whatever). She also talked about how Jane “lied about” Red John. She had the same look on her face, and calm speech that the secretary had when she was confronted…before she was killed, of course.

‘Roll Tide,’ the phrase that Kristina used when talking to the waiter in the first of the episode, was the last thing Red John said to Jane. Notice Red John also used present tense when speaking about Kristina. “She’s so fond of you” or something to that effect. RJ’s voice sounded female initially. Plus, when you go back to her previous appearance on the show, she knew entirely too much about Jane’s wife and daugther’s murders.