RJ has to be someone we saw in season 1. This show had no guarantee to run for as long as it did so with that in mind we have BP and McAllister. The second episode was written by Heller and we know he writes every episode tied to RJ so why this episode? Kinda random isn't it. He fits the description and subtle clues point to it being him such as he is mar, O'laughlin taking Grace to Napa Valley, the sheriff car at the end of Crimson Hat, and the appearance of him in general from pictures. I will be surprised if it is anyone else because Heller would have changed RJ Identity somewhere in the middle of the whole show.