Charles Cullen was supposed to keep patients alive. Instead, he became one of America’s most prolific serial killers. In Part 1 of this two-part series, Marina’s sister Lisa is back by popular demand to tell the story of Cullen’s troubled early life, his path into nursing, and the suspicious deaths that followed him from hospital to hospital. By the time Somerset Medical Center started questioning his use of the Pyxis machine, the true scope of the horror is only starting to come into focus.