Niels Hoegel, a 41-year-old German male nurse who is already serving a life sentence for two murders and three attempted murders, could have killed at least 100 patients with drug overdose between 1999 and 2005, the police officials and public prosecutors investigating the case have revealed.

A conviction in all these cases would make Niels Hoegel the deadliest postwar serial killer of Germany.

Reuters reports that Niels Hoegel was convicted in 2015 for killing two intensive-care patients with overdoses of some powerful medications. During his trial, Hoegel admitted to giving a drug overdose to patients to induce heart attacks in them. After patients suffered from heart attacks, he used to resuscitate them to prove his worth and be a “hero” in front of his seniors and hospital administration.

The strange motive for killing patients even perplexed the investigators, as this specific motive stood in complete contrast to other “angel of mercy” killing cases in which some nurses had killed patients to relieve them from their pain and suffering.

During his trial in 2015, Hoegel told the court that he gave drug overdose to patients out of “boredom”. He felt excited if a patient survived the attack, but felt upset in case the patient died of the heart attack.

According to the BBC News, Hoegel was finally caught when a nurse noticed a patient developing an irregular heartbeat in the clinic. The patient was previously stable, and at that time, Hoegel was in the room. Empty medication containers were also recovered from a waste bin in the room.

Germany serial killer: Niels Hoegl 'killed at least 100' https://t.co/NbItnrh6Jf — BBC News (World) (@BBCWorld) November 9, 2017

The investigation was widened in 2015 when Hoegel admitted that he had killed nearly 30 patients. In August, police investigations indicated that Hoegel might have killed at least 84 other patients.

“Eighty-four killings… leave us speechless,” Oldenburg police chief Johann Kuehme told reporters at that time.

“And as if all that were not enough, we must realize that the real dimension of the killings… is likely many times worse.”

In August, police exhumed 134 bodies from different cemeteries in Germany to test them for the presence of drugs, according to Reuters. Hoegel also told police that he is unable to recall everything he had done. Based on the results of the toxicology test, police have now said that Hoegel might have injected and killed no less than 100 people.

Police also revealed that Hoegel injected at least 38 people in an Oldenburg city clinic and 62 people at Delmenhorst. Oldenburg clinic data suggested that the number of deaths increased in the clinic when Hoegel was on duty.

Investigators believe Hoegel might have killed even more patients, but it is difficult to determine exact numbers, as the potential victims have already been cremated.

Fresh charges against Niels Hoegel are expected to be framed by next year.

[Featured Image by Joern Pollex/Getty Images]