This is a legitimate question and is currently under review in some states. Rather interesting.
I started reading more about this after that guy who requested that he be eaten and killed (in that order--he was served a bit of his own scrotum/testes while still alive) and found the guy who wanted to do that. So they did. So sure, it's murder. But the guys requested it.
Same thing with necrophilliacs, except there is no murder involved.