I think The Mentalist is too good of a show to not have a twist to the RJ storyline so I don't think they are just going to come out and say whoever Red John is. There are many good theories and clues for each suspect that could also be "red herrings" so I'm not particularly sure who he is but this picture of RJ killing looks alot like  Brett Partridge.
https://twitter.com/Eaglesk8r/status/384088228619247616/photo/1/large