Here is a quote from one of Heller's interview:  Question is in bold.  My comments are in italicized.  

In the first season I thought Red John was just a serial killer. But he’s evolved to be more of a Moriarty-type villain with this web of other people under him and lots of money. Can you give me your sense of how you see the character? 
The character is consistent in the sense that he has grown with time. He’s a bit like anyone who’s very successful at what they do, this superstructure grows up around you. Over time, he’s evolved as you say, from a serial killer to something more than that. I hate to use this analogy, and it may be an inaccurate one, but it’s like an actor. You start out by saying lines, then as you move up the ladder you start to think you’re more than a simple human being. Power attracts power and this is how great criminal psychopaths get power. 

There is only one that has grown with the show ... Bret Partridge.  He was there in the first episode, somewhat cocky but timid.  But in last's season's finale he is more in charge.  With that being said Heller said in another interview:

For you, as a writer, was it ever going to be someone else first?
No. Because like I say, as convoluted and as elaborate as the plotting might appear, you have to know exactly what you’re doing way before you do it. So things might seem mysterious or too complicated to work out what the hell is going on, but as these episodes unfold, the story will unfold itself in a clean and clear fashion. It was very important that Partridge die at this point in the story. It’s not just — he didn’t just kill him as an act-out.

So what is the reason that Bret is dead? I think it is for the audience to remove him from our list.  He isn't off mine.