Newly fascinated by the access a hospital gave him to the dead and dying, Harvey was soon able to secure a job as an orderly, despite having dropped out of school in the ninth grade (per All That’s Interesting). He hadn’t even been on the job long before he took his first life, using a pillow to smother an 88-year-old stroke victim. It was callous, cruel, and far from his last murder.

According to Oxygen, so many patients died on his shifts that co-workers jokingly called him “The Angel of Death,” though not suspecting (at least for many years) how close to the truth they were. But Harvey was not a mercy killer, despite later portraying himself that way. Even William Whalen, Harvey’s defense attorney wrote in a book about the murderer, that the “[b]ottom line was, Donald Harvey liked to kill,” reports FOX19.

In all, police can tie Harvey to at least 37 murders (for which he was convicted), though he confessed to as many as 57, claimed his attorney. In his 17-year-career between 1970 and his 1987 arrest, Harvey worked at a number of hospitals throughout the Cincinnati/Northern Kentucky area, killing patients via a staggering array of cruel methods, including arsenic, cyanide, and rat poisoning, as well as asphyxiation and even injecting their veins with air — far from merciful methods.

Harvey was sentenced to multiple sentences of life without parole but died in 2017 as a result of a severe beating by another prisoner.