A couple of thoughts.  First, I don't think RJ killed Jared Renfrew.  If you watch that scene carefully, the smiley face was painted on the right hand side of the bathroom, so it's not immediately visible when you walk in.  As you recall from the season 1 premiere, PJ knew that the killer was a RJ imposter because the smiley face was not the first thing you see when you walk into the room.  The killer is a RJ accomplice, possibly Bertram. 

Second, I'm pretty sure that the man who poisoned Rebecca is the real RJ.  The cops who escorted her did not recognize him, so I think we can rule out someone in CBI such as Bertram and Haffner.  Thomas McAllister makes sense in this regard since he's unknown outside of Napa Valley and is a sheriff, so he could have gained access into the building somehow. 

Third, I think Rosalind harker is still helping RJ.  I don't think PJ trusts her physical description of RJ since his very own list includes people who clearly don't fit the bill.