Former nurse Niels Hoegel was convicted of multiple murder and attempted murder of patients. Picture: Mohssen Assanimoghaddam/dpa via AP

Oldenburg, Germany - Numbers upon numbers - "death 1," "death 2," on and on until "death 100." A list of horrors. Each number assigned to a dead person, a victim, an individual's fate. Only Niels Hoegel knows how many people he murdered.

But the macabre truth is that the former nurse does not seem sure either.

Hoegel, who killed patients by injecting them with lethal doses of medication, testified that he could not remember 52 of the cases, but would not exclude his involvement. Maybe he killed those people, maybe not.

A lengthy trial against the serial killer ended in Germany on Thursday with the expected sentence of life. But many questions remain, along with the fear that the list of his victims may actually be longer.

In 85 cases, a court in the city of Oldenburg found the murders to have been proven. In 15 other cases, the regional court did not have "sufficient certainty" and so acquitted Hoegel. These rulings were based on the principle of "in dubio pro reo" - Latin for "when in doubt, for the accused" - said judge Sebastian Buehrmann.

This is particularly difficult for the victims' family members. "We let you go with uncertainties that must be so excruciating for you. We have to dash your hopes in this moment," Buehrmann told them.

Frank Brinkers is one of those relatives left with uncertainty. He lost his father.

"This is very, very bitter," said Brinkers, who struggled to keep his composure following the verdict. "I went through hell and it is hard to bear." He had hoped that his father's case would also be clear and irrefutable. "It was not meant to be apparently."

The main focus of the trial in the Oldenburg regional court was not on the final sentence. Instead, clarifying the facts and searching for the truth were the aspiration of the court, which opened the trial in October 2018.

"We will go to great lengths and do our utmost to look for the truth," judge Buehrmann promised at the time. This aspiration could not quite be fulfilled.

Sometimes the trial seemed more like a truth commission, the New York Times newspaper wrote last month, adding that Hoegel was leaving behind as many open questions as victims.

The now 42-year-old killed repeatedly from 2000 to 2005. Week after week, month after month, year after year. First, he carefully chose his victims. Later, he killed at random. The court repeatedly admonished against generalizing despite the high number of victims - these were all individual fates.

Former colleagues gave Hoegel many names. Some called him "Scythe Hoegel," "Death Hoegel" or "Resuscitation Rambo" because of his attempts to show off to other hospital staff by reviving patients he had apparently injected with lethal doses of medication that led to heart failure or other complications.

One expert described him as "psychologically depraved." But even the trial could not unequivocally clarify why this nurse did what he did. A craving for recognition, self-aggrandisement, narcissism - all have been ascribed to Hoegel.

Once he injected his patients with medications their condition would then quickly deteriorate, becoming life-threatening within seconds, setting off a hospital alarm.

Hoegel usually was the first in the room and would begin reanimation. He was good at that. And he wanted to excel in front of his colleagues and receive praise.

It was about having a sense of well-being, being in high spirits, building up tension and relieving stress. Right after the joyful birth of his daughter, Hoegel killed a person by administrating drugs.

"You wanted to achieve a sense of well-being by sending another person to their death" is how Buehrmann summarized it.

It's a case that has both shocked people across Germany and offered a glimpse into the mind and emotions of a serial killer. In the eyes of the victims' relatives, he should never be allowed to leave prison.