There has been many clues regarding the true identity of red john.
Some of the facts are:
Red John is a man. (As referred to by many; Rosalind, Lorlei,...)
He has or uses an odd voice.
He is right handed! (Several killings with his right hand)
He is an artist or had the touch of an artist. (Pilot Episode)
He is older than 30. (His first killing was in 1998 probably at the age of 20)
He is someone like Jane. He cares about Jane. He is NOT jane. (Shook his hand, saved him.)
He is challenged by Jane and he loves the chase.(Returning the case to Jane after murdering Bosco.)
He enjoys watching people die. Most importantly, he preys on their pain.
He loves tea.(Season 1 finale.)
He has very good electronic skills. ( Hacking into CBI computers and networks.)
He is someone very close to the CBI and has friends in the FBI.
Some Clues:
Kristina Fry told Jane that she spoke with his wife. His wife wants him to know that his daughter never woke up. Is she a real psychic? There are no real Psychics so she must be an accomplice. Red John might have wanted her to turn Jane but once he realized the opposite, he killed her.
It isn't anyone of his team. (Proof: Season 1 finale: Red John left the room when they arrived.)
Alex Jane( Patrick's father) is a good suspect. He taught Jane most the things he knows. Jane left him after the crystal incident. AJ wanted to get back to Jane by killing his family and waking him up from him pretending to be a psychic.
Those came to my mind at the spot. More evidence later
