I initially thought it was Bertram last week but now i'm convinced it's Partridge. 
We never saw a face in the morgue and I believe the skin on this body doubles arm was burnt to conceal the fact that Partridge doesn't have the tattoo even though he recited the tyger tyger poem. This I believe shows he is in fact Red John.  "Can't you see what this means??"

All his followers have the dots, but like stiles (his father figure) Partridge doesn't have the tattoo.

This is fantastically written and I take my hat off to everyone involved in the show