I believe that Red John could be a lot of people. The guy at the end of the third season who Jane shot could actually be the guy who killed Jane's wife and daughter. And all of the other murders could have been done by other suspects as well. But I think that Bret Stiles organized all of these people to kill by brainwashing them like he does with the people at Visualize. Ultimately Bret Stiles has organized his own group of serial killers to do anything he wants. That's my theory.