Niels Hoegel killed at least 100 people while working at hospitals in Oldenburg and Delmenhorst. Above, the Josef-Hospital hospital in Delmenhorts. (Wikimedia Commons)

A former German nurse confessed to the murder of at least 100 patients on the first day of his trial in the Oldenburg district court, according to the Guardian. The trial, which began on October 30, is the largest serial killing legal proceeding in Germany since the Second World War.

MSN reports that authorities first arrested Niels Hoegel, 41 years old, in 2005, when hospital employees in Delmenhorst caught him administering an unprescribed medication to a patient. In 2008, the court convicted Hoegel of attempted murder and sentenced him to seven years in prison, according to the Guardian. At the time, the authorities were still investigating several more suspicious deaths which they suspected were linked to Hoegel.

In 2015, under pressure from the families of the alleged victims, the district attorney prosecuted Hoegel again. This proceeding found Hoegel guilty on five counts of murder.

Later, during a psychiatric appointment, the former nurse confessed to 30 additional murders committed at the same Delmenhorst hospital at which he was apprehended in 2005, reports the Guardian. The confession prompted authorities to investigate additional suspicious deaths in a hospital in Oldenburg, where Hoegel previously worked.

All told, investigators attribute at least 36 deaths in Oldenburg and about 64 deaths in Delmenhorst to Hoegel, according to the Guardian. Authorities believe the death toll could include over 200 separate murders, but they worry that the cremation of many of the victims will stop them from ever ascertaining the exact number of deaths.

Authorities believe the death toll could include over 200 separate murders.

The new case against Hoegel, court officials say, intends to establish the exact scope of the killing spree that the nurse engaged in between the years of 1999 and 2005. Presiding judge Sebastian Buehrmann elaborated on the intentions of the court in a statement, emphasizing that court officials “will do our utmost to learn the truth. It is like a house with dark rooms – we want to bring light into the darkness,” as reports the the Guardian.

On the first day of proceedings, public prosecutor Daniela Schiereck-Bohlmann read out the names of the 100 victims and the charges against Hoegel. According to the Guardian, Hoegel “listened impassively, his head lowered.”

Buehrmann then asked the defendant if he planned to confess to the 100 murders committed in Oldenburg and Delmenhorst. According to the Mirror, Hoegel replied, “What has been admitted, that’s it. Yes.”

His quick confession came as a surprise to some. Christian Marbach, one of more than 100 co-plaintiffs in the trial and the relative of a victim, commented, “I didn’t expect it to happen today. We now have the chance to make some real progress.”

Hoegel followed the same procedure for each of the murders he committed, the Guardian reports. First, he injected a medication that triggered cardiac arrest. Then, he would attempt to resuscitate the patient. The prosecution argues that Hoegel’s murders stemmed from his desire to “show off ” his life-saving skills in front of his coworkers.