Dr. Royston Daniel = Red John.
Roy = the alias RJ uses
RJ would be confident & arrogant enough to use the shortened version of his name as his alias
Dr. Royston is a genius, a top hypnotist, very successful, very smooth, good looking, fits the description of RJ as per Rosalind Harker, and possesses skills of manipulation and hypnosis only very few talented people can perform (Kristina Fry was hypnotised to believe she was dead).
There are many other factors pointing to the strong possibility that he is RJ, however, it would take days to explain...
Check out S01 E18 , the only episode he appeared in..
In my opinion, I say, he's guilty!!
Let's see...
RJ could only be Kirkland, Mashburn or Dr. Royston in my opinion..
Minelli was hypnotised by PJ (see S01 E18).. I don't think it's possible to hypnotize RJ.. Many other factors which lead me away from Minelli as being RJ..
It would be too cliche is Stiles was RJ... I would be disappointed if stiles was RJ... Surely the producers are more creative than that...
Anyway, interesting to see what everyone else says..
I am a Mentalist fanatic!!