A chance remark in a Vienna wine bar led to a group of nurses in one of the city's oldest hospitals confessing to killing nearly 50 elderly patients to relieve the victims' suffering and lighten their own workload.

Austrian police confirmed Monday that a conversation between a doctor and a nurse at Vienna's Lainz hospital over a glass of wine alerted the doctor to what has been described as the biggest case of its kind in European history.Police have arrested four nurses who they say have confessed to killing 49 patients, all aged over 75, since 1983.

The patients were killed by injecting them with overdoses of medicine, including insulin usually used to treat diabetes, or by forcing water into their lungs to suffocate them, police said.