Okay, so let me start this off by saying I was so sure it had to be Partridge. He appeared in the first episode, his first words were "Red John enters here...", Jane called RJ a showman, Partridge walked Jane and co. through the details of the crime scene in the first episode as if he were on stage etc. That's until he died, and Bruno Heller says he is legit dead as well, which I was questioning considering we were all so sure it had to be him. When RJ took down Lisbon in the house, she appeared to be pulled back from behind. Lisbon was standing directly in front of a window, nobody came through that door which magically opened - no space. The only explanations are that it was someone outside the window, or Partridge attacked her from a grounded position. In S6E2, it was mentioned that Lisbon was unharmed, but she had been tasered. Partridge could easily have tasered her from the ground. But Heller says he'd dead. So, reluctantly, I'll have to leave that one.

Heller says the list is legit and if RJ is on that list, it's probably Kirkland, with him having some sort of paternal relationship with Stiles. None of the other 4 are disciples, despite how much everyone wants them (or just Bertram) to be.

But here's the ACTUAL theory. As someone who doesn't usually engage in 'conspiracy theories' or try and read too much into some hidden meaning that probably isn't even there, I thought I would indulge myself just this once... Right before RJ calls Jane (apparently from Lisbon's phone) in S6E1, Jane asks CBI Ron (the guy who is in the team and ALWAYS around, but NEVER has any lines lol) if he has seen Lisbon. He says no. Could be a hint. He also has his phone out at that point. He walks off camera, then Jane receives that phone call. When Jane was on the phone to RJ, the camera showed RJ holding his knife in his left hand and wiping blood off with his right. Neither of his hands were free, so how was he talking to Jane? Could have been using a headset, sure, but is it too weird to suggest that Lisbon wasn't killed by RJ because he wasn't there? I'm sure RJ could get his hands on the technology to make a phone call appear as if it is being made from another's phone. Ron could have attacked Partridge (who was clearly some kind of disciple or something), and left and gone back to CBI, and have the other person (Kirkland maybe) attack Lisbon. At CBI, Ron could have made that phone call to Jane after he got confirmation Lisbon was down (you don't have to be RJ to taser someone - anyone could do that). Also, when Lisbon's face was being painted, the assailant didn't use three fingers like RJ does (maybe because he was painting on a smaller space). This may all seem a little light, and it's probably Kirkland (even though he killed that guy in the hospital in a totally not RJ way). He was in that limo, that RJ is associated with etc but whatever, I'm clutching at straws now it's apparently definitely not Partridge. What do you think?