While working as a nurse over the course of 16 years, Charles Cullen killed at least 35 victims - although the suspected number is actually in the hundreds. He killed patients through overdoses and medical contamination in New Jersey and Pennsylvania hospitals. Cullen was arrested in 2003 and sentenced to 127 years in prison.
Amy Archer Gilligan "Sister Amy", serial killer. Born in 1868. Nursing home proprietor who killed at least 5 people, one of them her second husband, the other 4 were her patients. All died from poisoning, motive was to gain life insurance money. She may have killed more people, but that is still unconfirmed. Archer-Gilligan was sentenced to death in 1924, but was declared temporarily insane, and ended up in a mental asylum instead, were she died in 1962.