serial-killers-101:

In 1901-02, after she was in custody, Jane Toppan confessed to dozens of murders. She was extremely dangerous and more than a little unhinged: she would spend the rest of her life at Taunton State Hospital, dying in 1938 at the age of 81. Toppan grew up in an orphanage and then as a servant. Her killing spree started in 1885, when she was training to be a nurse. She took to experimenting with patients, using different combinations of medicines and chemicals to tweak their nervous systems and slide them between life and death. She also later admitted to being aroused by the process of killing. Toppan got away with her deeds for a while, especially when she entered private practice, after which she started racking up more victims by killing her landlords and later her foster sister. After killing an elderly man named Alden Davis and two of his daughters, the Davis family requested a toxicology investigation, which turned up traces of the poison Toppan had used. She was eventually charged with multiple murders, but she was found not guilty and declared insane.