Four nurses at Vienna's Lainz hospital murdered patients by injecting them with morphine and tranquilisers and drowning them in their beds They were caught in 1989 (Image: brandstaetter images via Getty Images)

A sinister group of nurses, chillingly known as the "Angels of Death", are believed to have killed up to 300 patients in a terrifying murder spree, administering lethal overdoses and drowning victims.

Waltraud Wagner and Irene Leidolf embarked on a seven-year reign of terror at Vienna's Lainz hospital from 1983 to 1989. They cruelly forced water into patients' lungs and injected them with excessive amounts of insulin and tranquilisers.

The malevolent duo were aided by two accomplices, Maria Gruber and Stefanija Mayer.

The serial killers confessed to police that they be

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