This is not my theory ! 

Listen closely to red john's voice when he answers Lisbon's cell phone and imagine Wayne Rigsby is talking. It's him. Also from a story telling standpoint, it's got to be someone on Lisbon's team for it to be A) shocking and B) good storytelling. Don't look outside of our main characters. And with the announcement that the actors playing Rigsby and Van Pelt leaving the show half way through the season and that Red John will be revealed before 2013 is over. Rigsby is Red John and he will kill Van Pelt before 2013 is over.