In extension to my theory on Gale Bertram below, I'd like to add that he seems to be the one person on the list, who really enjoys a challenge (a Red John trait). For example, in the episode where Jane is being held hostage, it's almost like he's testing Lisbon, to see how far she would go to protect Jane. After taking jurisdiction away from her, he sits back and waits for her next move (as if it was a chess game). In a way, it's almost like he's boasting, saying that he has Jane's life in his own hands, and he can easily influence and dictate what happens next. He's surprised then when Lisbon uses the media against him (his main flaw) but just like throughout the series, he generally respects anyone who can outplay him, and appears to really admire her actions(similar again to RJ who enjoys having worthy adversaries). Another point is, it was Bertram who informed LaRoche of Hightower's affair. Maybe she was was getting onto him somehow, and he felt threatened, so wanted rid of her. Being a showman, he had to do it theatrically in a way which could lead to Patrick somehow getting involved. Effectively his plan worked, because not only did he succeed in scaring off Hightower and remain anonymous, he also got to beat Jane again in another twisted battle of wits.
In the recent finale when Lisbon asks Jane how he knows that the murder was really  by RJ, Jane replies "because when it's him, he can feel it". When I first saw this, it took me right back to when Jane first meets Bertram. Straight away, Jane takes a disliking to Bertram and starts acting strangely..how many times does he turn down a case, because it doesn't feel right? Somehow I just feel it's connected, and that, that same gut instinct yelling out at him in the finale, was present when he first met RJ/ Bertram.
The meeting between Bertram and Lisbon (and Kirkland), was purposefully set up, in my opinion, so that people would start suspecting her to be an accomplice, and the tricks worked for some.  I think she's innocent and what Bob meant when he said "can we trust her" is that could they trust her to be telling the truth about Jane's progress in finding Red John. This would support my idea that Jane was trying and succeeding to worry RJ, by constantly hiding out in his attic, thus forcing Kirkland and Bertram to break rank and make the next move: break in and steal his research. Jane's on to them, I'm sure of it!

Finally, out of all the suspects, I think Bertram's the one that would shock the rest of the characters the most. Imagine your boss, a high ranking policeman, turning out to be the notorious serial killer you've been hunting for all these years! The reactions we'd see from Lisbon, the team etc, would make for amazing television. Plays out much better than a murderous sheriff or forensic tech which have all been done before eg. Dexter.
Thanks again for reading.