I think RJ is Reede Smith or Sheriff McCallister.  Why?  Because Bruno Heller gave us so many "clues" (in reality red herrings) as to why it could be the other 5 suspects of the final 7.  He is just distracting us from the real guy (and distraction is a big theme in the show).  So with Smith and McCallister, we really don't have much evidence to go by.  They are the two least obvious choices so thats why i would guess one of them.  Otherwise, how did they get narrowed down from the original 2 thousand something suspects to the final 7?  Clearly Patrick has reasons he thinks they might be RJ that we, the audience, don't know about.