The number one serial killer in the world...could now be a woman.

Prosecutors said Dr. Virginia Soares de Souza and her medical team administered muscle relaxing drugs to patients, then reduced their oxygen supply, causing them to die of asphyxia at the Evangelical Hospital in the southern city of Curitiba, Brazil. Investigators suspect she may have committed as many as 300 murders, which could make this women the number 1 serial killer of all time.

But then again we have....

Countess Elizabeth Báthory de Ecsed...

She was a countess in the Kingdom of Hungary. She has been labelled the most prolific female serial killer in history and is remembered as the "Blood Countess," though the precise number of victims is debated.

She was accused with 4 other collaborators of torturing and killing hundreds of girls, with some witnesses attributing to her over 650 victims, though they were only convicted for 80 murders.

Due to her rank, Elizabeth herself was not tried or convicted.