It found that Hoegel had administered lethal injections to patients at a hospital in Oldenburg, where he worked from 1999 to 2001.
However, as per Germany's judicial system, his jail term would not be amended given that the former nurse is already serving a life sentence, as it does not allow for consecutive sentences.
Prosecuters said Hoegel would try to successfully resuscitate his patients after inducing a heart failure or circulatory collapse, German broadcaster Deutsche Welle reported. But prosecutors have long said they believe he killed many more people, previous year putting the figure at 43 at least.
Kuehme added that if authorities acted sooner, some of these deaths could have been prevented.More news: Bangladesh Lead Australia by 88 Runs on Day 2 of Dhaka Test
Hundreds of bodies have had to be exhumed and re-examined as part of the investigation.
Hoegel's activity came to light in 2005 when a colleague witnessed him injecting a patient. But now they said that number may be short; that he had at least 86 victims.
Hoegel admitted to injecting patients with deadly drugs and then trying to revive them in an apparent ploy at playing hero, according to Al Jazeera Monday.
Kuehme said other medical workers at Oldenburg were aware of an elevated number of resuscitations, and initial indications of possible wrongdoing by the nurse in Delmenhorst emerged as early as April 2003.More news: Chow Yun-fat helps to clean up HK streets after Typhoon Hato
"Eighty-four killings. leave us speechless", Mr Kuehme said.
According to investigators, however, the real number of victims is likely to be many times higher, but it cannot be proven because some of the deceased were cremated.
His confession led the police to launch Kardio- a special forensic investigation to determine the cause of death of the patients.
The victims' names have not been released. He said he felt euphoric when he managed to save a patient and felt devastated when he failed to do so.More news: Trump lauds chief of staff reported to establish White House control system