Brett Partridge is absolutely Red John. He has been in the show since the Pilot episode as a Red John crime scene expert. In the (2nd?) season finale, there are a series of copy cat murders, copying Red John's style and putting videos up on the internet. If I remember correctly, Patrick knows Red John didn't kill those people, and Partridge disagrees. What better of a way for him to hide in plain sight than to disagree with Jane. And when Red John tells Jane the William Blake poem, you see that his body type is more similar to Partridge's than to any other suspect. I also recall Jane calling Partridge a ghoul at a crime scene once. Obviously Jane can see that Partridge enjoys murder/death a little too much.
More recently, when Lisbon goes into the house where Partridge appears to be dead, there is a room filled with birds. A Partridge is a bird, and its about the size of the birds that were in that house. I don't know exactly how to translate that symbolism, but to me it basically says, "Its Partridge." It was a small detail that most may not have noticed or picked up on, and its something that you can look back on later and say, "Holy crap that was so obvious!" or whatever..
Not to mention, what better way to eliminate yourself from a list of suspects than to do just that. Partridge was first to be crossed off the list and Jane thought nothing of it (as far as we know). He's been chasing down these other suspects only to uncover this secret society within law enforcement, and now Bertrum appears to be the prime suspect. I'm sorry, but there is no way in hell that Bertrum is Red John. You can see this twist coming a mile away. That being said, I think Partridge turning out to be Red John would be the most satisfying conclusion to the RJ storyline.
