This is not a theory, but just trying to clear something up:

A lot of people use the example of Rebecca being killed while in jail, saying that the person who killed her is Red John.  Is there any conformation that this was (FOR SURE) Red John?
I know that people assume that it is Red John because Rebecca is so excited to see him, etc., but isn't it possible that she was just excited that Red John had sent somebody to end her life?
I might have missed something, and maybe they said in the show that it was him, but I don't think that there has been any real evidence that Red John killed Rebecca.

Let me know if I'm wrong!