There were a lot of theories in the pre-reveal, and even to post-reveal of Red John, that Brett Partridge was Red John. Since the supposed events of episode 8, Jane has been ambiguous and said he "killed the man who killed his wife and children," so we've never had conclusive evidence to bury the hatchet on that one.

I think one thing the trial will set straight is in confirming whether the Sherriff was or was not in fact, Red John. Note one thing said by Jane when is he being reviewed (in the promo): "I love a good story." He sounds like a man ready to hear a fiction tale. And remember, the grand jury's "story" is the recognised version of events. And we know the recognised version of events is that Jane killed Thomas McAllister, who is Red John, as this is what Agent Fischer says in episode 10. So why is Jane so sceptical?  

What I'd love is for the panellist to repeat the events of episode 8, and for Jane to start laughing, and with a broad grin say, "You think that's what happened?"