a couple of days ago i read a theory that said that danny is Red John. A well elaborate theory, by the way.  So i re-watch that episode with danny, and i notice that danny has a voice very similar to Red John's voice. listen for yourself. 

http://www.youtube.com/watch?v=p9FXn-UKnS0

listen when danny says: "first compliment you ever gave i can recall"

i don't know about you guys, but his voice seems very similar to Red John's voice, adding that theory that i read, it seems that Danny really is Red John.