This is what I think....
There is no Red John. Red John is a creation That allows the CBI to harness PJ's psychic abilities in order to solve crimes. Let's not forget that Jane only joined the investigation/CBI group to get to Red John. If there was no Red John for Jane to pursue, then he would never of joined the force. Possibly, the Murder of Jane's Family was done by another person and the CBI created a fictional 'Red John' that gave Jane a reason to Join the CBI. Jane is a huge asset to the team as without him, they would be nothing (He solves nearly every crime). The Red John 'evidence' has all been put together by the team to manipulate Jane into thinking there is a real 'Red John' which encourages him to pursue RJ, which in turn, allows him to stay with the CBI.
Also, it's extremely unlikely (although it is fictional) that more than one person could be doing an inside job and working for RJ (or be RJ). The police and investigative force are not that corrupt, are they? Considering most of the seven suspects are working for police or CBI etc, it's likely they could be all working together considering the commonality of their jobs. This could reinforce my theory that they have all created Red John off a series of random murders and allowed Patrick Jane to pursue a Fictional Person in order to satisfy the CBI's needs.
Just a thought, but considering how the story is going at the moment, it's probley unlikely lol
