There have been multiple nurses that have killed people over periods of years.
It’s nowhere near as impossible as you seem to think it is.
Charles Cullen, a nurse, murdered dozens—possibly hundreds—of patients during a 16-year career spanning several New Jersey and Pennsylvania medical centers until being arrested in 2003.
William Davis, who worked at Christus Mother Frances Hospital in Tyler, Texas, fatally injected four patients with air.
Nurse Heather Pressdee pleaded guilty to three counts of first-degree murder and 19 counts of criminal attempt to commit murder.
Reta Mays, a former nursing assistant, killed seven elderly veterans with fatal injections of insulin at a West Virginia hospital.
The list sadly goes on and on and on. There’s even an entire Wikipedia article about it. And those are just the crazies that did for their own enjoyment.