The guys name who I think is Red John is Brett Partridge in the show. He Cleans up after the crime scenes. He plays in The Pilot Episode S1 E1 and also in S2 E23 Red Sky In The Morning. His Name is Jack Plotnick in real Life. If You watch very carefully at how Jane and Brett interact with eachother it is quite interesting. Its different then with other characters. They both seem to have a very deep disdain for one another which is strange considering they supposedly barely know one another or do they Know eachother and Jane just hasnt caught on yet. Unless its the opposite and brett is working for Jane not just in the CBI but as Janes disciple if Jane ends up being red John. Through all the episodes both scenarios would work as they both would have all the connections they need with the job positions they are in. And since bretts job is so under the radar but so connected to every crime scene it would explain why Red John knows so much. Think about it.

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.