The man known as the “bookkeeper of Auschwitz”, who in 2015 became one of the last people to be convicted for crimes in the Nazi genocide of Europe’s Jews during World War II, has died aged 96 in hospital on Friday, magazine Der Spiegel reports.

Oskar Groening had been sentenced to four years for his participation in the murder of 300,000  of the about 1 million victims who died in Auschwitz’s concentration camp before it was liberated by Soviet forces, but he had not started serving his sentence because authorities were said to be worried about his health.

Groening, who admitted he was morally guilty, had said he was an enthusiastic Nazi when he was sent to work at Auschwitz in 1942, at the age of 21.

He was born in 1921 in Lower Saxony in Germany and joined the Hitler Youth when the Nazis came to power in 1933.

His mother died when he was just four-years-old but his father was said to be a proud nationalist.

After the war Groening led a quite life in Lueneburg Heath in Lower Saxony, working at a glass-making factory until he retired.

The 96-year-old’s lawyer had argued Groening was too frail to go to prison. He submitted a request for clemency in early March.

A spokesman for the public prosecutor’s office in Hanover confirmed it had been notified of Groening’s death from his lawyer.