Ray Haffner

His first episode..... "The Little RED Book"

His most recent episode...... "The RED Barn".... lots of clues revealed this episode.

RJ always seems to know PJ's plans after he shares his idea with Lisbon. Lisbon could be RJ, but more likely she shares the info with Haffner, who then is able to stay one step ahead.

He was/is a member of Visualize. He couldn't/wouldn't confirm or deny being at the farm back at the time frame of the two murders (two murders if you believe the vet's daughter's story).