I'd be interested in hearing Psychological or Psychiatric reports that might substantiate one way or the other criminal mindset on this.
IMO, If this crime is premeditated (my thinking is that the criminal mind usually fantisizes about this type of crime before acting on it), I would think the perpetrator goes into it with the mindset that he either wants to rape the victim, or that he goes into it wanting to rape and kill the victim. Whatever give him the biggest thrill.
I can't imagine that the wacked out decision to murder on top of rape is related to a "death penalty either way" mentality.
FTR, I don't care what the cost to taxpayers is, the longer the sentence the better.