Just on a technical note to clear that "ante-mortem" and "peri-mortem" business up. I used the term "peri-mortem" to make clear, a lot of killers of this type use dismemberment as killing method ("during the kill"). It is not, that he, for example cut an arm off (using a tourniquet) and then end the game by quickly slashing a throat. They go on as long as they can hold the victim alive during the process. Ante-mortem would be more the classical torture with coup de grace. Different thing, because it tells us about a different mindset.
Peter