Donald Harvey started working in hospitals at just 18, initially as an orderly at Marymount Hospital in London, Kentucky. It was here that he confessed to his chilling first crimes, admitting to the murders of at least a dozen patients during his ten-month stint. His actions were not limited by patient profile; his victims varied widely in age, race, and background but were typically cardiac patients.

Harvey claimed his killings were acts of mercy for the terminally ill, although he also conceded that some were driven by personal anger towards the victims. His methods were gruesomely varied, employing arsenic, cyanide, insulin, and even more direct means such as suffocation and tampering with medical equipment. Notably, he also used poisons to incapacitate or kill those close to him outside the hospital, including a lover he suspected of infidelity, his lover's father, and neighbors. His long-hidden spree was eventually uncovered after an autopsy of a man who had died unexpectedly in the hospital revealed cyanide in his system.

This discovery led to Harvey's arrest, where he confessed to the murder. Further investigation prompted by suspicious nurses and a local TV anchor revealed Harvey might have been responsible for many more deaths, perhaps as many as 70. In a bid to avoid the death penalty, Harvey pleaded guilty to multiple counts of murder in 1987, resulting in several life sentences. His criminal activities finally ended with his own death in prison in 2017, following a severe beating by a fellow inmate. This inmate was later convicted and sentenced for Harvey's murder.