Giulia Tofana was a professional poisoner in the 17th century who marketed her special recipes to wives who wished to murder their husbands. Once she was apprehended, Tofana estimated that she was accountable for having supplied the poison in 600 deaths, making her one of history's most prolific assassins.
Source Materials:
https://www.ncdv.org.uk/giulia-tofana-serial-killer-or-heroine/
https://aspectsofhistory.com/giulia-tofana-power-poison/
https://allthatsinteresting.com/giulia-tofana
https://thecrimewire.com/multifarious/The-Most-Notorious-Woman-Killer-in-History
https://www.ancient-origins.net/history-famous-people/giulia-tofana-0014131
https://www.ranker.com/list/life-of-giulia-tofana/genevieve-carlton
https://www.womensrepublic.net/aqua-tofana-giulia-tofanas-secret-ingredient-to-a-happier-life
https://unbelievable-facts.com/2021/04/giulia-tofana.html
https://www.syfy.com/syfy-wire/giulia-tofana-the-italian-serial-poisoner-who-became-a-legend
