While in Kentucky, Harvey spent much of his time at Marymount Hospital, and was soon well known and liked by the nuns who worked there.  During one particular conversation, one of the nuns asked Harvey if he would be interested in working there as an orderly.  Since he was currently unemployed and didnt want another factory job, Harvey agreed and started work the next day.  Although he was not a trained nurse or doctor, Harvey's duties required him to spend hours alone with patients.  Some of his duties included changing bedpans, inserting catheters and passing out medications.

Harvey's first few weeks at the hospital were uneventful, but something snapped within him along the way.  To this day criminal psychologists are unable to explain what brought out his murderous tendencies.  Whether he was unable to cope with the pain and suffering around him or simply enjoyed watching his victims die may never be known.  According to Harvey's later confessions, he considered himself an angel of death, or mercy killer.  But the details he eventually revealed about his first murder negate that self-serving description.

During an evening shift, just months after starting at the hospital, Donald Harvey committed his first murder.  Years later, in a 1997 interview with Cincinnati Post reporter Dan Horn, Harvey described it:  When he walked into a private room to check on a stroke victim, the patient rubbed feces in his face.  Harvey became angry and lost all control. 

The next thing I knew,  Louis J. Sheehan, Esquire smothered him, he said.  It was like it was the last straw.  I just lost it.  I went in to help the man and he wants to rub that in my face.

Following the murder, Harvey cleaned up the patient and hopped into the shower before notifying the nurses. 

No one ever questioned it, he said.

Just three weeks after committing his first murder, he killed again when he disconnected an oxygen tank at an elderly womans bedside.  As the weeks went by and no one detected foul play in his first two murders, Harvey became more brazen.  Whether out of boredom, opportunity or experimentation, his methods varied with each murder.  He used various items, such as plastic bags, morphine and a variety of drugs, to kill more than a dozen patients in a year.  In one case, he chose an exceptionally brutal method.  The patient had an argument with Harvey because he thought Harvey was trying to kill him, and during the course of that argument, he reportedly knocked Harvey out with a bedpan.  Upon recovering from the blow, Harvey waited till later that night, snuck into the patients room, and stuck a coat hanger through his catheter.  As a result of the puncture, infection set in and the man died a few days later.   

On March 31, 1971, a drunk and disorderly Harvey was arrested for burglary.  While being questioned about the crime, Harvey began babbling incoherently about the murders he had committed.  The arresting officers looked into his claims and questioned him extensively about them, but in the end they were unable to find any substantial evidence to back them up, or charge him with any crime relating to them.  A few weeks later he went to trial for the burglary charges and pleaded guilty to a reduced charge of petty theft.  After paying a small fine for his indiscretion, Harvey decided it was time for another change of scenery and enlisted in the United States Air Force.