Ok here it is. Red John is not one but two people.
Red is of course our ubersexy red hottie Grace. She loves sex and haves uber hot sex with all the victims.
John is obviously Cho, when his name is translated to english. Cho is cool as cucumber. He likes to kill and kills all the victims.
Together Red and John have uber-hot asian redhead sex. Like Bonnie and Clyde, Batman & Robin.
Did I mention that Red is that ubersex-hottie Grace?
