During a court session in the German city of Oldenburg, Niels Hoegel, 41, confessed to the murder of over 100 patients at two hospitals in northern Germany, the Guardian reported. 

Hoegel is suspected of having killed 36 patients in Oldenburg and another 64 in nearby Delmenhorst from 1999 and 2005.

Hoegel is currently serving a life sentence in prison for murder after the first day of his trial in the biggest serial killing case in Germany’s post-war history.

His fellow nurse discovered that Hoegel injected a lethal dose of the drug to one of the patients. However, he appealed and continued to work while his case was considered in higher instances.

The German nurse was arrested and sentenced to seven and a half years in prison in 2009 for several attempted murders.

In 2015, the killer nurse was sentenced to life imprisonment for two murders and a series of attempted murders. However, during the process, Hoegel confessed to his psychiatrist that he killed about 30 people. The police has launched a new investigation in this regard and criticized the management of medical clinics in Oldenburg and Delmenhorst for showing indifference to the high mortality rate.