A 94-year-old former guard at Auschwitz went on trial in Germany on Thursday, accused of being an accessory to the murder of at least 170,000 people - the first of four such court cases that could be the last due to the very old age of the defendants.The three men and one woman accused are all in their nineties and will be tried over the next few months, starting with Reinhold Hanning in the western German city of Detmold.Hanning was 20 years old in 1942 when he started serving as a guard at the Auschwitz death camp in occupied Poland where more than 1.1 million Jews were killed by the Nazis.Prosecutors said he voluntarily joined the armed SS at the age of 18 and participated in battles in eastern Europe during the early stages of World War Two before being transferred to Auschwitz in January 1942."The defendant is accused of having worked as a guard at the Auschwitz concentration camp in Poland between 1943 and 1944. Through his work there the defendant is believed to have assisted the many thousands of killings. Against this backdrop, he is accused of assisting in the murder of at least 170,000 cases," Detmold regional court spokeswoman Anneli Neumann said.Accused by the prosecutor's office in Dortmund as well as by 38 joint plaintiffs from Hungary, Israel, Canada, Great Britain, the United States and Germany, Hanning will face the accounts of contemporary camp witnesses.One of them is Erna de Vries, who in 1943 at the age of 23 was deported to Auschwitz along with her mother. Considered a "Jewish crossbreed" as her father was Protestant, she was saved from the gas chamber and transferred to a labour camp.Investigations by Germany's special Nazi war crimes office in Ludwigsburg show that Hanning served as a guard at Auschwitz until at least June 1944.While Hanning admitted to his guard duties in a statement to the prosecution, he denied involvement in the mass killings.