Just a thought;

I have a strong feeling that Red John somehow changed his identity.

What about this. Jane's wife marries Jane because she is really smart and so is he. As we know they are both kinda similar just RJ is bad and PJ is good. So when PJ bashes RJ who is actually his wife, she kills their daughter and fakes her own death. Then she does the unthinkable because she knows PJ will recognize her; she gets a sex change/

So she becomes Bob Kirkland and goes from there. Y'all might hate on this theory but when I'm right y'all can feel my wrath.