A former Nazi officer known as the "bookkeeper of Auschwitz" goes on trial in Germany next Tuesday, possibly the last SS member to face punishment after most escaped justice.

Oskar Groening, 93, will be tried on "accessory to murder" charges in 300,000 cases for his role in the deaths of mostly Hungarian Jews deported to the death camp in 1944.

His trial -- 70 years after the liberation of Germany's concentration camps at the end of World War II -- is the last currently scheduled for a former Nazi.

About a dozen preliminary investigations have been launched, but the others are unlikely to go to trial given the advanced age and poor health of the suspects.

Media interest is expected to be intense in Lueneburg's trial near the northern city of Hamburg, where some 50 Auschwitz survivors will appear as co-plaintiffs or witnesses.

Groening has insisted he "never gave so much as a slap" to a prisoner, but prosecutors argue he was a cog in the Auschwitz death machine that claimed more than a million lives.

The defendant volunteered for the Waffen SS in 1941 and was transferred to Auschwitz in Nazi-occupied Poland the following year.

There his job was to account for the cash stolen from inmates, sorting the money by currency, counting it and sending the funds on to Berlin.

At times he was also stationed at the railway platform, where prisoners were divided on arrival, and either taken directly to the gas chambers or sent to work as slaves, prosecutors say.

Groening has apologised in a string of media interviews for serving as an Auschwitz guard, but insisted he was personally innocent of murdering deportees.

"The SS was a criminal organisation, that much is clear. But back then I though I was serving Germany," he told the daily Hannoversche Zeitung last year.

"For me it was nothing different to what was happening at the front. I thought what happened in Auschwitz was right. That's the message I had been fed since I was 10."

Groening's trial illustrates a last push by German justice to pursue surviving Nazi war criminals.

Despite post-war Germany's efforts to atone for the war and Holocaust, relatively few Nazis were jailed by a court system initially staffed by many judges and prosecutors who themselves were tainted by the regime.

For decades, they targeted only suspects linked to specific atrocities, usually demanding rare eyewitness testimony.

At landmark mid-1960s Frankfurt trials, Auschwitz deputy chief Robert Mulka was sentenced to 14 years in prison, while the man in charge of supplying the lethal gas Zyklon B received eight years.

In total there have been 6,656 convictions since 1945, on charges ranging from perjury to murder. More than 90 percent of sentences were less than five years, according to historian Andreas Sander.

Just 49 former Auschwitz SS officers were among the convicts.

Groening, a witness in three trials, had himself been cleared by a court in 1985.

A 2011 case set a new legal precedent, when a Munich court sentenced to jail the former Nazi death camp guard John Demjanjuk, a former Ukrainian citizen who had spent years in the United States.

Judges accepted that Demjanjuk was an accessory to the murder of almost 28,000 Dutch Jews, based on the fact that he had worked at the Sobibor extermination camp in Nazi-occupied Poland.

If the courts had applied the current criteria all along, "tens of thousands of German citizens" should have been in the dock, said legal expert Cornelius Nestler at the Demjanjuk trial.