My theory is simple and based on dubbers.
Although I am a proud sustainer that RJ may be Brett Partridge, I must acknowledge what follows:

Just ran into a list of the Italian dubbers of the serial (which you can find here: http://it.wikipedia.org/wiki/Personaggi_di_The_Mentalist#Criminali) and could not help but notice that the Italian dubber of Red John (as confirmed here in the right side box, you can find "Voce italiana: Massimo De Ambrosis" which means "Italian voice: Massimo De Ambrosis" http://it.wikipedia.org/wiki/John_il_Rosso) also happens to be the dubber of two other characters in the serial. Those are Timothy Carter (Fake RJ, eventually killed by PJ) and ....DRUM ROLL.... Robert Kirkland.

Even if you are not native Italian speakers, you can find this out on your own by clicking CTRL+F with your active browser window to look for words within the page you're visiting.
You can enter "Massimo De Ambrosis" in the first link I provided just to find 3 occurrencies which are those I mentioned.
("doppiato da" = "dubbed by")

Could somebody please confirm this for other languages as well? I was not able to find the names of the french, spanish, german, and so on dubbers to confirm the theory.