A German federal court has rejected a former Auschwitz death camp guard's appeal against his conviction for being an accessory to murder, a decision greeted Monday as setting an important precedent for future prosecutions of Holocaust perpetrators.

Oskar Groening, now 95, was convicted in July 2015 of being an accessory to the murder of 300,000 Jews and sentenced by a court in Lueneburg to four years in prison. Judges found that he knew Jews were being slaughtered and supported the killings through his actions.

The Federal Court of Justice's decision to uphold the former SS sergeant's conviction boosts ongoing cases against other suspects and raises the possibility of further investigations against others who served at Nazi death camps or in other functions.

"It's very exciting news," said Efraim Zuroff, the head Nazi hunter at the Simon Wiesenthal Center in Jerusalem. "The door is open."

Groening, who has been dubbed the "accountant of Auschwitz," testified at his trial that he oversaw the collection of prisoners' belongings and ensured valuables and cash were separated to be sent to Berlin. He said he witnessed individual atrocities, but did not acknowledge participating in any crimes.

Presiding Judge Franz Kompisch ruled last year, however, that Groening was part of the "machinery of death," helping the camp function and also collecting money stolen from the victims to help the Nazi cause, and could thus be convicted of accessory to the murders committed there.