German prosecutors say a nurse who was convicted of killing patients with overdoses of heart medication had at least 43 victims.

Niels Hoegel was found guilty last year of two murders, two attempted murders and one count of serious bodily harm at a clinic in the northern town of Delmenhorst.

The crimes came to light in 2008 after Hoegel was convicted of attempted murder in another case. Authorities subsequently investigated hundreds of deaths.

Prosecutors said Friday that Hoegel likely committed at least 37 homicides in Delmenhorst and an additional six in nearby Oldenburg.

Oldenburg prosecutors say they have indicted six former staff members at the Delmenhorst clinic who failed to report concerns about suspicious patient deaths. They face up to 15 years in prison, if convicted of negligent manslaughter.