He roamed the University of Cincinnati campus with a loaded gun. When his rage overflowed, the brainy microbiology major would open fire inside empty buildings, visualizing a wall clock or other object as a person who had done him wrong. By the mid-1970s, Bruce Ivins had earned his doctorate and was a promising researcher at the University of North Carolina. By outward appearances, he was a charming eccentric, odd but disarming. Inside, he still smoldered with resentment, and he saw a new outlet for it. Several years earlier, a Cincinnati student had turned him down for a date. He had...