During my senior year in medical school, a madman in town randomly attacked several people with a hammer, slaying two and injuring eight others. Our chief of plastic surgery, a noted reconstructive surgeon, repaired the killer’s flexor tendons after he had attempted suicide by slitting his wrists. “He can hold a hammer again,” our teacher wryly noted after the successful trauma surgery. But with that bit of dark humor, he reinforced to us students a revered tenet of medical ethics—the principle of non-maleficence. That is, a doctor should never in the course of his or her professional work willfully do harm to another person. And that goes for the least among us, even a vile murderer.