"Two can keep a secret if one of them is dead."  It's implausible that so many people know Red John's identity, and yet it remains the best kept secret of all time. At this point, there would at least be rumors, whispers of Red John's identity.  

Every week Jane catches the culprit with almost nothing to go on. Jane has hundreds of pages RJ files. Jane knows the specific locations and times of the RJ murders. Jane has a finite list of suspects.  Come on, there is NO way Jane should still be this clueless.  Process of elimination and old fashion police work should get the list down to about 10. I'm sure most of them have solid alibis for at least one of the RJ murders. Then Jane can have the rest under surveillance, play mind games with them, etc.

Oscar Ardiles...sure....why not? 

I think Red John is Kristina Frye. She is one of the few people that have the same skills as Patrick and appears to manipulate people with ease. She is also one of the only people that Patrick has had problems reading.

All the evidence points to Red John being a man.. the witness statements, the rape... But if we think about RJ's track record he has always used accomplices and at least one of his accomplices convinced the CBI team that he was RJ himself, therefore I don't think RJ has to be a man. I think RJ has to be someone who can manipulate men to pretend to be RJ. The rape was also not committed by RJ but by the man Lorelei killed in the last episode.

Women are more hated as criminals, it is somehow more shocking and dramatic (which is what the producers are looking for) for RJ to be a woman, especially when all evidence appears to suggest he is a man.

Kristina'a storyline was unbelievable. She was sure that RJ would not hurt her when she spoke of him on TV. This is not a conclusion a normal person would make from looking at the evidence. She then 'vanished' whilst under the guard of Van Pelt (who has also gone a little crazy since spending time with Kristina in my opinion). There was no apparent disturbance she just vanished which incriminates one of them or both of them to me. She is also the only person (to my recollection) who has survived a RJ kidnapping aside from PJ. Her appearance after her abduction was equally strange and unbelieveable. It is also incomprehensible that PJ would have just given up on her after the few minutes of trying to make her talk. She is the only survivor of RJ and she was very close with PJ, you would think he may at least visit her in a later episode.

RJ is a master manipulator with the same skills as PJ. Kristina shares her brilliance with Patrick in manipulation.

The letter RJ left to PJ when he killed his family taunts him about not being 'a real psychic'. Kristina is adamant that she is 'a real psychic.' Obviously real psychics do not exist so Kristina is not to be trusted.

Kristina and PJ shared a connection that explains their fascination with each other on another level - neither like to be outsmarted and both like game-playing.

Kristina appears to be about the same age as RJ may be and we didn't find out about her background.

RJ would not have spared Kristina's life. Also Kristina has sat happily out of view for a few seasons now so that we all forget her.