I suspect, that BP was RJ in Hellers mind till season 6. But then fans figured it out too quickly, so he switched to another character which was there from the beginning. Less obvious plan B, I might say.
That is why nothing is explained. Clues don't entirely match. And the whole thing is rushed to the end. Even the last episode was about nothing most of the time. Unimportant events, feeling up the episode till the last showdown. Heller simply did not know, how to connect all those clues to McAllister, so he filled the episode with nothing really.
This is the only good reason for such a poor end of RJ.