19th & 20th Century:  The BUTLER did it!

21st century:  The CREEPY FORENSICS GUY did it!

Bret Partridge as Red John would be the BIGGEST "untwist" CBS ever produced [otherwise known as the "ass pull" on tvtropes -- you know, like out of your ass because the writer can't be creative enough] 

HERE'S SOMETHING DIFFERENT:

Bret Partridge fancies himself a Sherlock Holmes type, though Jane outwits him at every turn -- BP is book and fact smart but lacks mentalist skills and knows it -- and he looked like he was gonna cry in Desert Rose -- clearly BP seeks Jane's approval.

I would DARE say BP might actually be one of the GOOD GUYS who might have been conducting his own mini-investigation on the side.  Mostly, it seems he was killed BUT if BP faked his own death -- he did it to avoid RJ or to help CATCH RJ.  Now THAT would be a good twist since it's expected that THE CREEPY FORENSICS GUY DID IT!