In the exhilarating Fast, Cheap & Out Of Control, one-of-a-kind documentary auteur Errol Morris took four seemingly disparate subjects—a lion tamer, a mole-rat specialist, a robot scientist, and a topiary gardener—and discovered ingenious and unexpectedly moving ways to connect them. He considered adding a fifth, Boston engineer Fred A. Leuchter Jr., but as his disquieting Mr. Death suggests, the man's enigmatic mind demands its own forum. With his now-signature melange of multiple film stocks, stylized photography, and hypnotic carnival-esque music, Morris introduces Leuchter, a bespectacled loner who made an odd business out of designing more humane execution devices. Though a death-penalty proponent, he was appalled by the unnecessary suffering inflicted by primitive electric chairs, unreliable lethal-injection methods, and rickety gallows. His singular occupation, "execution technologist," would be interesting enough, but it was his acquired knowledge of gas chambers that led to another, more disgraceful endeavor. Ernst Zundel, a Canadian neo-Nazi indicted for publishing two books (Did Six Million Really Die? and The Hitler We Loved And Why) which violated hate-crime statutes, recruited Leuchter to conduct experiments at Auschwitz to prove that cyanide gas was not used in concentration camps. His segue from death-row humanitarian to Holocaust denier would seem like a shocking transition, but as Morris compiles his fascinating interview footage, the common thread seems to have more to do with vanity than hatred. The most harrowing aspect of Mr. Death is that Leuchter comes across as strangely innocent in intent, a dispassionate and hopelessly deluded man of science. For that same reason, he also makes an impenetrable subject for a documentary, though Morris' dynamic technique helps compensate for some dull stretches. (His 1903 footage of an elephant being electrocuted is an especially startling find.) Revealing but never judgmental, Mr. Death taps into the disturbing world of a man whose moral vacancy and hubris lead to tragic possibilities.