This is a bit long shot but...
We all know what happened in episode 23 of the 2nd season.

Red John: Do you know who I am?
Patrick Jane: Yes...
Red John: Tiger, tiger, burning bright....

And remember. Patrick Jane kept it as a secret even from his team. He claimed that Red John didn't say anything to him when he saved his life.
What happened now, in the season 6 opener, is the following: Brett Partridge, while dying, was reciting the same song.

My question is: How did Brett Partridge know about the connection between The Tyger song and Red John himself? He could have identified Red John simply by saying "It was Red John," but he used that recitation instead.
For me, this is a big clue.
Opinions? Maybe I have overlooked something...