He confessed to authorities that he killed up to 40 patients during the course of his 16-year nursing career. But in subsequent interviews with police, psychiatric professionals, and journalists Charles Graeber and Steve Kroft, it became clear that he had killed many more, whom he could not specifically remember by name, though he could often remember details of their case. Experts have estimated that Charles Cullen may ultimately be responsible for over 300 deaths, which would make him the most prolific serial killer ...more on Wikipedia