Here's my theory plain and simple. The voice of Red John to me in every episode that he has spoke in is to high pitched to be anyone other than Partridge. I know, I know, Partridge is supposed to be dead, but, if he's actually dead then why in the next episode did it not show anything about it. It was just kind of looked over and on to the next suspect. Also when it showed his supposed dead body, it just flashed on the screen for a minute and no one could tell if it was actually Patridge or not. Partridge( if I'm correct) has been on the Mentalist since episode 1, he's been there from the beginning and he'll be there at the end......as Red John!