I've read a lot of theories, and I was one of the ones who tought it was Brett Partridge...
People still thinks it's him but I don't think it's Partridge.
In the episode 1 season 6 the real Red John was hiding in the bathroom.Nobody noticed that the bathroom's door was closed and when Lisbon turns it was opened?
That's why she looks scared and suspicious when stares at it...it also seems she is grabbed from behind and she is giving his back at the window, she mantains the same position since when she get up, this means Partidge body is in front of her...how could him get up and grab her from behind withouth being noticed?
Sure, it's television and everything is possible but now I think that the theory that RJ is Partridge is poor..

Sorry for my english.