Skyrezo
Warning. If you haven't seen season 6 of the Mentalist yet, you shouldn't read this. Contains spoilers.
Red John, everybody was busy searching for him, finding out who he was. And when they finally found him, he got killed immediately. Nobody ever questioned how he became such a terrible person? What was his life like before he started killing?
Just a little peek inside the head and past of Red John before he brutally started killing people. Also, an idea of his thoughts during his time being a serial killer.