Unfortunately, the exact number of people Cullen killed is unknown. However, after his arrest in December 2003, he told homicide detectives he murdered as many as 40 patients during his 16 years as a nurse. Some experts believe that Cullen is responsible for at least 400 deaths, but we may never know without further admission from him.

Although he confessed to killing up to 40 patients, only 29 could be confirmed.

As part of his plea agreement, Cullen will not face the death penalty for his crimes since he promised to work with authorities to help identify other potential victims. He is currently serving 18 consecutive life sentences at New Jersey State Prison in Trenton and is not eligible for parole until June 10, 2388.

In 2013, Cullen spoke publicly about his actions for the first time on 60 Minutes. During the segment, titled "Angel of Death," he said he didn't consider himself a serial killer. However, he later accepted the moniker. As for his motives, Cullen reflected on his first nursing job in which he worked at a burn unit.

"There was a lot of pain, a lot of suffering, and I didn't cope with that as well as I thought I would," he stated.

After being asked why he killed patients, including those who would recover and weren't terminally ill, Cullen said, "It's difficult for me to go back in time and think about what things were running through my mind at the time." Cullen later admitted that he didn't get pleasure from the killings and claimed he thought he was helping since the patients "weren't suffering anymore."