Red John is Jane's brother in law, Danny.

According to Patrick Danny is, from episode 302, a great con artist and a psychopath.
Was mad when he took his sister away from him. It was the only good think to happen to him.
He doesn't seem to be mad at Red John at all despite killing his sister.
Very competitive with Jane.
Fits the physical description. Taller than Jane. Athletic like we have seen in episode 302 when escaped the cop.