Former nurse Niels Hogel hides his face during a court appearance on two murder charges in 2015, in Oldenburg, Germany. Monday, German authorities he is suspected of killing at least another 88 patients. File Photo by Carmen Jaspersen/EPA

Aug. 28 (UPI) -- A former German nurse already in prison for murder is now suspected of killing dozens of other patients with lethal drug combinations, a three-year police investigation released Monday found.

In February 2015, Niels Hogel received a life sentence for two deaths and several attempted homicides of intensive care patients at Delmenhorst hospital in northern Germany.


In an investigation, though, police believe he's involved in another 88 deaths after analyzing patient files and exhuming more than 130 bodies in Germany, Poland and Turkey. A total of 84 additional deaths linked to the drugs were uncovered in the investigation.

The murder spree began during his employment at a hospital in 2000, in Oldenburg, and continued at a hospital in Delmenhorst until he was caught in the act by a colleague on June 22, 2005.

"As if all that were not enough, we must realize that the real dimension of the killings by Hogel is likely many times worse," Oldenburg Police Chief Johann Kuhme said during the news conference.

More possible victims' bodies were cremated.

"The death toll is unique in the history of the German republic," chief police investigator Arne Schmidt said.

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Schmidt said he was "speechless" about the crimes, which were committed randomly and against patients in critical condition.

According to police, Hogel would inject patients with a cardiovascular drug to bring on medical emergencies that would then require him to resuscitate them.

Five drugs used were ajmaline, sotalol, lidocaine, amiodarone and calcium chloride, police said. With sick patients, overdoses can lead to life-threatening cardiac arrhythmia and reduced blood pressure.

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Six employees of the Delmenhorst clinic were charged with manslaughter through failure to render assistance. And a investigation into neglect at the Oldenburg hospital is ongoing.

"The murders could have been prevented," Kuhme said. "People at the clinic in Oldenburg knew of the abnormalities."

Hogel, 40, was sentenced in 2008 to more than 7 years for attempted murder. Afterward, a woman who'd followed the case contacted police to say her mother may also have fallen victim to Hogel.

In January 2015, Hogel confessed to administering 90 unauthorized injections, of which 30 had been fatal because he had been unable to reanimate the patients. He said he felt "fully responsible" for the 30 deaths but denied any other killings.

He was convicted of two murders through evidence from bodies exhumed determined at the time six died from the drugs administered.

New proceedings against Hogel are scheduled for next year.