"Why didn't Voldemort die? The killing curse rebounded, so he should have died. Why didn't he? At the end of Goblet of Fire he says that one or more of the steps that he took enabled him to survive. You should be wondering what he did to make sure that he did not die - I will put it that way."
But now the speculation is over. Fandom need fret no more. Now at last, I can reveal – Voldemort's Secret!