On Monday, German serial killer Niels Högel was charged with 97 counts of murder for allegedly killing upwards of 100 patients by injecting them with drugs and trying to revive them. The former nurse admitted to acting "out of boredom" and said he was trying to impress his colleagues. It's believed that he killed 38 patients in his care between 1999-2002 and another 68 patients between 2003-2005.

The 106 verified murders are only a legal statistic, however. Many other killings could not be proven because the victims' corpses were cremated. Plus, it's unclear how many attempted murders occurred. Evidence suggests that Niels' was able to resuscitate two out of three patients that he drugged.

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Deutsche Welle

The murderer had already been serving jail time for killing six patients by giving them a cocktail of medicine that causes heart failure or circulatory collapse. He was first sentenced in 2008 to seven and a half years in prison for attempted murder, before being handed a life sentence in 2015 for six counts of murder.

Throughout the investigation, police found that the hospital failed to report the shocking increase in fatalities when Niels was working. "If the people responsible at the time, particularly at the Oldenburg clinic but also later in Delmenhorst, hadn't hesitated to alert authorities — for example, police prosecutors — Högel could have been apprehended sooner," Oldenburg Police Chief Johann Kühme said.

So far, Niels has confessed to 30 of the murders and is due in court next year. If convicted, he will be one of the most prolific serial killers in German history.

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