Just one thought.After rewatching season 6 episode 5 episode in the 38:42 minute when kira opens the door to red john (if he is the one that killed her)  you can see from the shadow that he has all of his hair.Food for thought.

http://www.whoisredjohn.com/See-a-theory-Red-John/13248

And this is my theory if you are interested.