Heres a little tid bit to consider.
In episode 8 Season 2, His Right Red Hand, we might actually see Red John as he passes Rebecca and poisons her. Her expression is telling that it is in fact him.
If you take this into consideration, there is a lot look at here that MIGHT shed some light. The weight, stature, walk, and the back of the individuals head is made apparent.
All these things could be cosmetically altered ore changed, sure, but maybe not.
Though the body type doesnt match Brett, everything else does no?
https://www.youtube.com/watch?v=1otRlA3PedI Heres the clip, though its super dark,. I studied this scene from the actual episode for quite awhile, hope that shed a bit of light~
