Brett is just like Dexter Morgan from "Dexter" for those who don't know, Dexter is a TV show about a serial killer that works with the police, He is a blood spatter analyst so he can tell what happened to dead victims, ie. where they were shot. When we first saw Brett he was sort of explaining Red John's M.O(how he kills), he explained it... Jane said it himself that he enjoyed his work too much, so he enjoys deceiving the police, so that would explain Lorelei saying Jane and RJ were both deceitful. 

At the least... Brett has to be the copycat that helped Jane after he was abducted by the copycats. If you watch YouTube videos that change the pitch of Red John talking, you'll see that it sounds like Jane. So a part of me believes Jane may be RJ.