He calls always Agent Lisbon in the thirteen episode of season 5 ``Teresa``. In the first episode of the sixth season, Red John said to Patrick Teresa can't come to the phone. I never saw in the serie another person than Haffner who call the first name of Agent Lisbon. He's certainly the serial killer because he is the only person who call the first name of Agent Lisbon.
How do you find this theory?
plausible
unlikely