I have a very strong feeling that it's CBI Ron. As stated before, Bruno said that RJ is more of a Where's Waldo in the series and that's exactly what Ron has been from the start. He is always popping up, even in the season finale when Patrick killed who he thought was RJ at the time in the mall.

From a writers perspective, why would they have Ron hanging around here and there for 6 seasons? This isn't the type of show that has the same extras just hanging out in the background week after week, so there has to be a reason he is there. Ron just blends into the crowed and nobody suspects him of a thing, even when he seems a bit fishy such as this season already and in the past.

Just my thoughts to add to the conversation.