BERLIN -- German officials expect to bring new charges against a nurse already serving a life sentence for two murders after determining that he might have killed another 84 patients, if not more, a prosecutor said Tuesday.

Oldenburg state prosecutor Martin Koziolek said he expected his office would be bringing more charges by early 2018 against Niels Hoegel, who gave patients overdoses of heart medication and other drugs because he enjoyed the feeling of being able to resuscitate them.

Additional convictions could affect Hoegel's possibility of parole, but there are no consecutive sentences in Germany.

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More than that, bringing additional cases to trial would help determine exactly what happened in those killings and provide some closure for families, Koziolek said.

"These were not all terminally ill people," he said. "Many were on their way to recovery."

Niels Hoegel masks his face with a folder on his arrival in the courtroom at the regional court in Oldenburg, Germany, December 9, 2014. Fabian Bimmer / REUTERS

He declined to give the ages of the victims or any other details about them, citing German privacy regulations.

Hoegel, now 40, was convicted in 2015 of two murders and two attempted murders at a hospital in the northwestern town of Delmenhorst and was sentenced to life in prison.

During his trial, Hoegel had said he intentionally brought about cardiac crises in some 90 patients in Delmenhorst by giving them overdoses. He later told investigators that he also killed patients in a hospital in nearby Oldenburg.

Hoegel worked at the Oldenburg hospital from 1999 to 2002 and in Delmenhorst from 2003 to 2005.

As part of a wider investigation involving both hospitals, police and prosecutors reviewed more than 500 patient files and hundreds more hospital records. They also exhumed 134 bodies from 67 cemeteries.

They questioned Hoegel six times. They said he had been willing to talk about the other cases and "confessed to a large number" of them, but that "in most cases, he couldn't concretely remember manipulating treatment, but he also didn't rule it out."

Authorities said Monday as a result of the new probe, they'd unearthed evidence of 84 additional suspected murders, and were awaiting toxicology results on 41 other fatalities.

Oldenburg police chief Johann Kuehme on Monday said there could have been even more killings linked to Hoegel, but further investigation was not possible because the bodies had been cremated.

"Eighty-four killings ... leave us speechless," Kuehme told reporters. "And as if all that were not enough, we must realize that the real dimension of the killings by Niels H. is likely many times worse."

He also faulted local health authorities for being slow to act, saying if they hadn't hesitated in alerting authorities, Hoegel could have been stopped earlier.

Authorities are already pursuing criminal cases against former staff at the two medical facilities.