Jennifer Hall of Kansas swears—and has long sworn—she isn’t a serial killer. In 2002, the respiratory therapist was working at Missouri’s Hedrick Medical Center when nine patients died suffered cardiac arrest on her watch before she was placed on leave. This month, she was charged with first-degree murder in one of those deaths, of 75-year-old Fern Franco. According to the probable death statement, Hall “knowingly caused the death of Fern Franco by administering unprescribed Succinylcholine and Morphine.” Hall’s lawyer maintains that she did not have access to the substances found in Franco’s body. Throughout Hall’s five-month stint as a respiratory therapist at the hospital, the facility logged 18 “code blues,” which mark instances of cardiac or respiratory arrest, whereas it had only been recording one each year prior. John P. Rice, a professor of mathematics in psychiatry at Washington University School of Medicine, said the number of code blues logged during Hall’s time at the hospital represented “a pattern that would happen less than one in a million times.”