In March 1999, Cullen took a job at the burn unit of Allentown's Lehigh Valley Hospital, where he murdered one patient and attempted to murder another. One month later, he voluntarily resigned from Lehigh Valley Hospital and took a job working in the cardiac care unit at St. Luke's Hospital in Bethlehem. During the subsequent three years, Cullen murdered at least five patients and is known to have attempted to kill two more. On January 11, 2000, he once again attempted suicide by lighting a charcoal grill in his bathtub, hoping to succumb to carbon monoxide poisoning. Cullen's neighbors smelled smoke and called the fire department and police. He was taken to a hospital and a psychiatric facility, but returned home the following day.