Nurses deal with drugs every day. Most do so professionally, safely, reliably. A very few abuse them, getting high or selling them for a profit, mostly opiates. And a tiny minority — a handful in the history of nursing — turn medicines into a murder weapon. One such nurse was Charles Cullen, who is the subject of my book The Good Nurse. A former Navy electronics technician who used his technical acumen to enable his crimes and avoid detection, Cullen got away with medical murder in at least nine hospitals over the course of his 16-year career. He eventually admitted to 40 murders, but experts familiar with the case believe that number is low, perhaps by several hundred.