Case closed:

* "The Great Red Dragon" is the episode in which Red John's identity is revealed.

* Jordan Harper is the writer of this episode. Harpers first episode as writer on The Mentalist was
"Redline" - the episode where Walter Mashburn was introduced for the first time.

Jordan Harper  is the one picking up his storyline ofc and leading us to the revelation that:

RJ = HE IS MAshburn

I admit it was a bit of cheating checking out who was the writer and putting it together that way.