Employing a hypnotic jump-cut style that appears heavily influenced by Oliver Stone's ''Nixon,'' he creates a kind of instant X-ray psychoanalysis, fixating on Leuchter's creepy mechanistic indifference in a way that allows us to fixate on what it's camouflaging: Leuchter's infatuation with death, and with his own power over it. In a minor but revelatory detail, Leuchter confesses, rather proudly, that he drinks 40 cups of coffee a day. That's not just overstimulation -- it's heavy drugs. In ''Mr. Death,'' this designer of ''humane'' killing machines is revealed to be a bureaucratic mortality junkie, perhaps the most passive-aggressive man of the 20th century.
Just when you're certain that you've got the rat fink pinned, the movie takes an astonishing turn. It follows Leuchter as he's tapped, in 1988, by a neo-Nazi Holocaust denier on trial in Canada (where the spreading of ''false news'' was, at the time, a crime) to do a study debunking the reality of the gas chambers at Auschwitz. In extraordinary video footage, we see Leuchter in the death camp, chipping and scraping away at the 50-year-old extermination-room walls for evidence of cyanide; he's like Poindexter in the Temple of Doom.
When his samples yield no poison, he concludes that the atrocities didn't happen, and he becomes a star on the Holocaust-denial lecture circuit. Fred Leuchter is just one deluded figure, but by the end of this great and chilling sick-joke documentary he stands as a living icon of the banality of evil, a man who blanks out the world around him, replacing it with his own ego, always denying his desire to annihilate.