Kirkland is a decoy IMO, he'd be far too obvious to be RJ. He strikes me as someone out for Justice, much like PJ. 

I'm thinking it could be CBI Ron, or he could be an accomplice. He works for the CBI, and we've long suspected that RJ has an insider at the CBI, or works for the CBI himself, given how he's able to access their servers and even access the building himself (like when Rebecca was murdered in season 2). Also, the old saying is "keep your friends close, but your enemies closer". How better to analyse and watch Patrick, than to spend each day in the same building? 

For all we know, the list given in season 5 could be a decoy, Bruno may have said that the list was real, but he's backtracked on things before, and this could be another bluff.

To end, in season 4, when RJ's at Rosalind's house, we see RJ's arm holding a teacup, and he's wearing a suit much like Ron wears, is a similar build to Ron (in arm thickness) and has a hairy hand, Ron is hairy.