Oskar Groening was convicted in 2015 of being an accessory to the murder of 300,000 Jews at the Nazi concentration camp in occupied Poland during the Second World War.
The man known as the "Accountant of Auschwitz" died Friday at the age of 96, according to Germany's Der Spiegel.
Groening (pictured left in the German army and right at trial in 2015) was in hospital when he died and had yet to begin his sentence.
Despite his conviction, the start of his sentence was delayed by legal wrangling and his ill health.More news: 5 things to know about Mizzou's first-round opponent in NCAA Tournament
A former Nazi SS guard dubbed the "Bookkeeper of Auschwitz" has died aged 96 almost three years after his conviction for being an accessory to murder, German media said on Monday.
Yet, of the camp's 6,500 SS personnel who survived the war, fewer than 50 were ever convicted.
"As fate would have it, [Groening] too has now escaped justice, casting a shadow of sorts on the judicial processes", he said.
"Their victims never had any appeals, nor did their tormentors have any mercy, consequently these perpetrators don't deserve either", the group said in a statement.More news: The Hemenway Trust Co LLC Acquires Shares of 4710 Starbucks Co. (SBUX)
German prosecutors deemed Groening to be fit enough to go to prison as long as there was appropriate medical care.
His court battle was viewed a landmark as it was one of the last major cases surrounding the Holocaust.
Oskar Groening had previously been sentenced for his role in some 300,000 murders during the Holocaust.
One million European Jews were slaughtered in Auschwitz, only a sixth of the number who died as part of the Nazi regime overall.More news: Thomas helps Lakers to win over LeBron, Cavs
During the trial, Groening asked for forgiveness while acknowledging that only the courts could decide when it came to criminal guilt.