Wikipedia: Locusta was a Roman serial killer during the 1st century AD.Locusta was born in the Roman province of Gaul. In AD 54, she may have been hired by Agrippina the Younger to kill the Emperor Claudius, possibly with a poisoned dish of mushrooms. In 55, she was convicted of poisoning another victim. When Nero learnt of this he sent a tribune of the Praetorian Guard to rescue her from execution. In return for this she was ordered to poison Britannicus. She succeeded on her second try, Nero rewarding her with immunity from execution while he lived, rewarding her with a vast estate and even sending students to her. Seven months after Nero's suicide, Locusta was condemned to die by Galba in January 69. Apuleius described her life and she is mentioned by Suetonius. Juvenal also mentioned Locusta in Book 1 of his satires.
EXCERPT: Then the ancient Roman poisoner, Locusta, who lived in the time of the Emperor Nero, and whose name and memory are justly condemned to infamy, invented poisons that would either kill in an hour or at periods varying from a day to six or twelve months. Nay, she could produce death by the smell of a nosegay, and many an aromatically poisoned flower has proved a precursor of the tomb.
[“Poison and Poisoning.” The Wisconsin Daily Patriot (Madison), Sep. 21, 1851, p. 2]