Not sure if this has already been written off as a theory but from the most recent episodes it seems to me the most likely suspect would be Patrick Jane's father (Alex Jane). Partially, from the way everyone talks about how similar Patrick and Red John are, and the whole picking a memory straight out of Jane's head in the last episode.
Originally I thought it was Brett Partridge as it seemed as though it was him who saved Jane when those kids took him captive, but now I think that would be far too likely.
