My first theory is posted here

http://www.whoisredjohn.com/See-a-theory-Red-John/9976

And in my personal opinion that is the only suspect it can be, to give this great show the final meeting it deserve, Bruno Heller said that people would be dissapointed when they learned who RJ was, of course he's gonna say that , without lying , you just have to read all the great theories here in this forum, you can't please us all, we all have our favorite !

RJ has to be some one who was in the show very early on, the team behind The mentalist, didnt know if it was gonna be a hit or be shut down after one season, and that kinda narrows the list a bit, but again they can have changed their mind about who RJ is as the show gained so popular, so they had to put in some more suspected characthers, to keep us the audience on the edge, but if they are gonna stay true to their first choice I guess Partridge is de ideal character , you can read my reasons for this using the link at the top.

Heller has himself talked about  similarity between RJ and PJ relationship and Sherlock and Moriaty, I guess he means the cat and mouse game they are playing, and we know that RJ's hope for PJ friendship exposes him, how RJ can think that PJ wanna be friends with the person who killed his family shows that RJ in his criminal brilliance , is a person without human perspective, yes he knows have to seduce and manipulate , but as a psycopat he cant really connect to normal human feelings, and in a sick way, maybe he think he did PJ a favour killing off his family.

For me only one person can portrait such a devious, creepy person and play it with an intensity that blows you away !