I don't know if it is Bertram, but I just wanted to point out that other than Red John and Patrick Jane, Bertram has been the only one to drink tea. (Out of the viable suspects, maybe the mother of a victim once had tea with Jane, or something, I don't recall) Also, they made Bertram's tea pretty prominent and obvious in the scene. (Season 3 finale, Strawberries and Cream part 2, when Lisbon tells Bertram that they know where Madeleine Hightower is, and give him the hotel address.
