I've always had a sneaking suspicion it's one of Lisbon's brothers. We know one is tommy, apparently another one is named james; however, the last is unnamed. Why would they give us the other two but not name the third. He has to play a role sometime otherwise they wouldn't mention him. Their father was abusive which could make him have violent tendencies and we all know Lisbon's controlling so red John may kill women who remind him of Lisbon to gain control over them the way Lisbon had control over him. It would explain why so many red John disciples have an obsession with doing things revolving around Lisbon and not just Jane.
Examples: bringing RJ Lisbon's head
Mashburn sleeping with her if he's a disciple,
Ray haffner and Kirkland talking to her being friendly,
And O'Laughlin shooting her instead of high tower which was his original mission.
Plus I suspect Lisbon either knows or has her suspicions because of how weird she's been acting and giving he weird looks behind Jane when he mentions getting closer to RJ. It's not Lisbon but she's worried because it might be her little brother. Hence why she wants justice instead of death if Jane gets to red john. Jane may have met him in the past or Lisbon introduced them off camera which would explain hand shaking. Just a theory that popped in my head so probably not enough evidence I just wanted to put it out there for bragging rights if I'm correct.
