Not so much a theory on who RJ is, but rather some observations.
1. When Kirkland killed Jason Lennon, he asked Lennon if he recognized him. This clearly shows that this was BOB Kirkland, desperately looking for someone with a connection to his twin brother.
2. When Kirkland kills Jason Lennon, Kirkland describes himself as a "friend" and the killing seems almost compassionate in its execution.
These 2 things seem pretty incongruous from what we saw of Kirkland in last night's episode - someone out to destroy Red John for having taken his twin brother away.
Now we don't know if Michael Kirkland is still out there somewhere, but I think that observation #1 above pretty much rules out him being the one that killed Jason Lennon.
As for who actually IS Red John, this is just a theory, but let's look at some possibilities:
Bret Stiles COULD be Brett Partridge's father.
Bret Stiles COULD have all kinds of influence and connections through Visualize members within law enforcement - enough to influence them to provide SOME protection to his son. He could even have some pull through the "Tyger Tyger" organization. Pull that his son could easily be aware of.
These connections and influence COULD have been what Partridge was looking for when he said "Tyger Tyger" to Lisbon as she found him - looking for some assistance in faking his own death. When such assistance was not offered, he tasered her when she looked away. The next law enforcement to arrive responded affirmatively to Brett Partridge's "Tyger Tyger" reference, thereby assisting him in faking his own death.
If you watch the episode where Brett Stiles helps Jane rescue Kristina Frye, Stiles seems genuinely concerned with stopping, but not necessarily catching and punishing Red John - the way a father might want his adult son to stop behaving badly, but also want his son to avoid what the father considered too harsh a punishment.
So my overall theory is that Brett Partridge is Red John. He is Bret Stiles' son and he has used his father's connections to protect himself, though he is not without the power of persuasion himself. He uses his fathers connections but sees himself as ultimately surpassing his father in importance (as do Red John's followers). This also explains his need for attention, his need to make the Red John painting the center of every one of his crime scenes. As the son of a cult leader, he could never HOPE to garner such attention himself, so he tries that different tactic to get the attention he so desperately craves.
