Red John has cult following him, like Bret Stiles and his accompliances. Brett Partridge is one of them, like Craig O'Lauglin was. It's no one from his team, because that would be just too weird for mainstream tv show and Kristina Frye has now some mental problems and that disqualifies her. Also  I don't believe in RJ=PJ theory, just because that would be too big twist.