Made by documentary maestro Errol Morris, Mr. Death: The Rise and Fall of Fred A. Leuchter, Jr. (1999) is about as good as it gets — and I mean not just for a documentary, but for any movie. Roger Ebert gave it his highest rating:
Like all of Morris’ films, “Mr. Death” provides us with no comfortable place to stand. We often leave his documentaries not sure if he liked his subjects or was ridiculing them. He doesn’t make it easy for us with simple moral labels. Human beings, he argues, are fearsomely complex and can get their minds around very strange ideas indeed. Sometimes it is possible to hate the sin and love the sinner.
Readers of my blog know I don’t put a tremendous amount of stock in Rotten Tomatoes, but Mr. Death is the only film I can recall with a 100% Tomotometer score. It is a great and fascinating movie. Not available via streaming, but highly recommended and worth seeking out.