I think that Red John is somehow related to Van Pelt.
 My guess is that Red John is Van Pelts brother. Van Pelt has never said that she has no siblings so it's possible and Van Pelt doesn't really like to talk about her family. I think her brother did something bad (to her or someone else) and she doesn't want to think about him anymore. If my theory is true Red John must be someone who Van Pelt has just heard mentioned and never actually seen or who she has seen only a glipse of so she couldn't reconise him. He has brobably changed his name so he couldn't be so easilly reconised.
 In the episode 2/10, Throwing Fire, Van Pelt tells Rigsby she has no sister but at the same time she looks a little awkward like she was uncomfortable with the subject. There is definately something about her family that she doesn't want to talk about. I'm not sure if Van Pelt knows or suspects this somebody she knows (who ever it is) to be Red John, but I just think that Red John is somehow connected to Van Pelt weather she knows it or not.
 And Van Pelt has red hair and red is always a bad thing in Mentalist :D