I think we may have been given another clue about Red John during the final 10 minutes of the show.  Lisbon was looking at a computer display with a map of California and each of the cell phones she had tapped (P-Partridge, B-Bertram, H- Hafner, M-McCallister, K-Kirkland, and S1 and S2 for Smith and Styles).

If we the map was correct and each of the suspects actually had their cell phones, then we can probably rule out a few folks.  Kirkland was in LA, and Styles and Smith were both in the San Francisco area.  Even McCallister appeared to be about 45 minutes away from the house where Partridge was killed.  The two suspects who appeared to be near the home were Bertram and Hafner.

Since the show went out of it's way to point the finger at Bertram, I think Hafner was the one most likely to be at the house ... if it was, in fact, Red John and not one of his accomplices.