6. Gesche Gottfried
Gesche Gottfried worked as a nurse in 1800s Germany and was responsible for killing 15 people by poisoning them with arsenic between 1813 and 1827. She typically mixed the poison in the victim’s food.
Not just that, she also killed her own parents, her fiance, two husbands, and her children! She was the last person to be publicly executed in the city of Bremen.