Red John is Lorelei.  Jane shakes her hand, the first time they meet in the season four finale.  Despite the fact that many believe Red John is a man, Lorelei is able to easily manipulate others, especially men with her beauty.  Jane and Lorelei are both searching for the killer of their family, and share qualities.

 Lorelei: (referring to Red John) God, you're just like him, you know that? Relentless manipulation.
Jane: I am nothing like him.
Lorelei: How would you know? I know. I only wonder why the two of you didn't become lifelong friends the moment you shook hands.