This could be wrong (probably is) but here's my theory: I don't know exactly who Red John is but I feel like the 7 suspects know who he is and he is seeking some type of revenge on them. The 7 may have been part of some group or cult that destroyed his life years ago. They must have thought he wasn't a problem anymore so he was able to disappear and become Red John. Now, before he can kill Jane he must expose and destroy those who hurt him as a form of revenge and to show Jane that no one is innocent and people deserve to be destroyed. However, the 7 suspects are trying to fight back. It would explain why Partridge was only around on the Red John cases, Kirkland was trying to find out all the info he could, and Bertram/Reede/McAllister met (in order to hide their secret).

As for individual suspects for this theory my list would be:

Walter Mashburn- We never found out what his dark secret was. Plus, he is one of the main suspects outside the 7.

Ellis Mars- I really thought he'd be on the list. He is supposedly psychic, the clue from the Renfrew crime scene, and he seemed to be a viable counterpart to Jane in the episode.

Max Winter- He tried to push Jane over the edge and turn him into a murderer with partial success.

The theories are based on my own thoughts and info from The Mentalist Wiki. Again, just an idea, but it might be crazy enough to be right.