Niels Hoegel was convicted by a court in the city of Oldenburg in June 2019.
The Federal Court of Justice said it had thrown out his appeal, finding no procedural or other errors with the verdict.
Hoegel injected patients with overdoses of drugs because he enjoyed the feeling of being able to resuscitate them.
Sometimes he succeeded in bringing them back, but in at least 87 cases the patients died, making him what is believed to be modern Germany’s most prolific serial killer.
Last year’s verdict came on top of a 2015 conviction for two murders and two attempted murders, for which he was already serving a life sentence.
The trial court noted in its verdict the “particular seriousness” of Hoegel’s crimes, a finding that all but ensures he will remain incarcerated after the 15 years of a life sentence typically served in Germany is up.
Hoegel worked at a hospital in Oldenburg between 1999 and 2002 and at another hospital in nearby Delmenhorst from 2003 to 2005. The killings at issue in last year’s trial took place between 2002 and 2005.
In all, Hoegel was tried in Oldenburg on 100 counts of murder, but the court found him not guilty on 15 counts for lack of evidence.
Pleas are not entered in the German system but during the seven-month trial, Hoegel admitted to 43 of the killings, disputed five and said he could not remember the other 52.
The federal court also rejected an appeal from a co-plaintiff against Hoegel’s acquittal in one of the cases where the court could not find sufficient evidence.
