BERLIN — A German nurse serving a life sentence for murdering two of his patients is believed to have killed at least 86 people entrusted to his care, officials said Monday (Aug 28), in what they described as an imagination-defying series of crimes.

The nurse, identified as Niels Hoegel, was sentenced to life in prison in February 2015, after he confessed and a court in the northern town of Oldenburg found him guilty of administering overdoses of heart medication to some patients in an intensive care ward in Delmenhorst. He was convicted of two counts of murder, two counts of attempted murder and causing bodily harm to patients and is serving his sentence.

During his trial, the former nurse had also confessed to intentionally inducing cardiac crises in 90 of his patients, 30 of whom he said had died. That prompted officials to launch an investigation into the deaths of some 130 of Hoegel’s former patients. The results were presented Monday in Oldenburg.

At least 84 of the convicted killer’s former patients were found to have died after suffering from injections of five different forms of medication, Johan Kuehme, chief of police in Oldenburg, told reporters.

Authorities are waiting for the results of another 41 toxicology reports, the results of which could drive the number of confirmed deaths even higher, he said.

“The realisation of what we were able to learn is horrifying,” Mr Kuehme told reporters. “It defies any scope of the imagination.”

Hoegel, now 40, told the court at the time that he had enjoyed trying to revive the patients. But his efforts did not always succeed, leaving some to become his victims.

The special commission, launched in October 2014, after Hoegel’s confession, combed through evidence that included more than 500 patient files. It based its conclusions in part on toxicology tests on the remains of 134 possible victims, who were exhumed to see if they contained traces of the chemicals the nurse had confessed to using.

It found that Hoegel had administered lethal injections to patients at a hospital in Oldenburg, where he worked from 1999 to 2001.

The investigation also found that although the high number of patients dying under Hoegel’s care was noticed by other staff members in Oldenburg, no action was taken to understand why.

As suspicions began to swirl around the nurse, he was later transferred from a ward to a position in an anesthesiology unit, according to the public broadcaster NDR.

There, a doctor who worked with him at the time told Hoegel that his services were no longer wanted, because he was always forcing himself into the spotlight when trying to revive a patient, the broadcaster reported.

Nevertheless, after the nurse quit his job in Oldenburg, he was issued a recommendation that bore no indication of any concerns about his ability to carry out his duties, the broadcaster said.

In December 2002, Hoegel then took up a new job as a nurse at the hospital in Delmenhorst.

In 2005, a senior physician at the Delmenhorst hospital, acting on concerns about the nurse, looked at the death records and medicines administered by Hoegel and came to the conclusion that he may have killed as many as 100 people. He alerted authorities.

Hoegel later confessed to killing two patients at the clinic, which led to his conviction by the court in Oldenberg. But the conclusions of the investigation announced Monday make clear those deaths were just the tip of the iceberg. Authorities are continuing to look into how he was able to kill so many people for so long without being stopped by hospital administrators.

In October 2016, prosecutors brought charges against six employees of the hospital in Delmenhorst, on suspicion of negligent manslaughter, for failing to take action despite their suspicion regarding the nurse’s actions.

A related investigation into hospital personnel in Oldenburg is continuing, but no one has been charged.

Directors and senior medical staff in Oldenburg are similarly suspected of failing to take action and issuing a reference that made no mention of concerns about his behaviour during his tenure at their clinic. THE NEW YORK TIMES