YEKATERINBURG, Russia — On the outskirts of this burly industrial center, off a road like any other, on a nowhere scrap of land — here unfolded the final act of one of the last century’s most momentous events. A short way through a clearing, toward a cluster of birch trees, the killers deposited their victims’ bodies, which had been mutilated, burned and doused with acid to mask their origins. It would be 73 more years, in 1991, before the remains would be reclaimed and the announcement would ring out: the grave of the last Russian czar, Nicholas II, and his family had been found. But the story does not end there.

No New Yorker is privy to as many secrets of the dead as Dr. Charles S. Hirsch. During nearly two decades as New York City’s chief medical examiner, he has quietly overseen autopsies on more than 100,000 people, hoping to learn something more about the way they lived, and why they died. After a long run marked by few major controversies, Dr. Hirsch, 70, now finds his objectivity and independence being questioned because of his review of a single autopsy — on the body of James Zadroga, 34, a New York City police detective who died in New Jersey last year.