I want to try and look at this like a mentalist (if I can manage). The statement made by the actor (undisclosed) who will play RJ may have been including a clue in it. As you know, almost all characters who're accused to be RJ are accused for their actions, behavior and suspicious moments. So, we can say that there have been "certain elements" that made us suspect that those guys may be Red John.

However, the actor says: I though "I WAS" a red herring. I don't know if I'm thinking too deep but he's putting his entire character on the table and call it a red herring. He doesn't say that he thought his actions or behavior is red herring. And the only one who can be identified according to this statement is CBI Ron. Maybe wrong but it was worth to mention. Of course, I have to deny the list in order to come up with such a theory. Have fun people!