From doctors to opera singers, teachers to truant schoolchildren, the extermination of European Jews was the work of roughly 200,000 ordinary Germans and their helpers. Years of research -- not yet complete -- reveal how sane members of a modern society committed murder for an evil regime. Walter Mattner, a police secretary from Vienna, was there in October 1941 when 2,273 Jews were shot to death in Mogilyov in Belarus. He later wrote to his wife: "My hand was shaking a bit with the first cars. By the tenth car, I was aiming calmly and shooting dependably at the many...