November 13, 1967 - Kristen Gilbert

A nurse at a Veterans Affairs hospital, she exploited the trust and access her position afforded her, using a method — epinephrine injection — that mimicked natural cardiac events and went initially undetected. The victims were patients in a setting defined by medical care, making the breach of that context as significant as the acts themselves. Her case raised lasting questions about oversight in medical institutions and the particular danger posed when the capacity to harm is built into a professional role.

From Wikipedia

Kristen Heather Gilbert (née Strickland; born November 13, 1967) is an American serial killer and former nurse who was convicted of four murders and two attempted murders of patients admitted to the Veterans Affairs Medical Center (VAMC) in Northampton, Massachusetts. She induced cardiac arrest in patients by injecting their intravenous therapy bags with lethal doses of epinephrine, commonly known as adrenaline, which is an untraceable heart stimulant.