I've got to go with Lisbon's gut, and suspect Haffner. The guy rubs me the wrong way. We know he matches the physical description, he's the correct age, and he was at the barn when the murders happened. He's a member of visualize (So Brett Stiles would know him well, plus we know that Stiles knows who RJ is).  

Also it would be ironic (and typical of this show) if it was Lisbon, not Jane, who figured out who RJ was. PJ solves Lisbon's cases. maybe Lisbon has solved Jane's?