My theory is that Red John is actually no single person but is an organization with insiders in the government (e.g. FBI agents, and others) in various industries.  There was an RJ industries in one episode.  The organization has a tremendous amount of resources and interests.  The "Red John" murders have been carried out by different people in the organization.  The murders have been committed for fun, revenge, intimidation, or other reasons.  I also suspect that the organization is working on powerful mind control techniques.  In one episode, a woman in black went into a hotel room to kill Hightower.  When she was discovered, she jumped out the window to her death.  She must have under some kind of mind control to do this.  Also, when Christina was discovered in a catatonic state, it is likely that the organization did some kind of mind control experiment on her.