"The sadistic killer had sex with his several victims after their deaths."
If I am not mistaken Ted Bundy also practiced this ghoulish behavior. He would revisit the corpses of his victim before they began seriously putrefying and engage in intercourse with them.
If it wasn't Ted, and I think it was, then it was some other homicidal maniac. But then who are we to judge? Necrophilia is just another life style choice, minus the homicide of course, and we must accept these different lifestyles or be thought of as bigots.