On a snowy winter day in 1991, Lu Gang, a slightly built Chinese scholar who had recently received his Ph.D. in plasma physics, walked into a seminar room at the University of Iowa’s Van Allen Hall, raised a snub-nose .38-caliber Taurus pistol, and killed Professor Christoph Goertz, his thesis adviser; Robert A. Smith, a member of his dissertation committee; and Shan Linhua, a fellow Chinese graduate student and his rival.