A 93-year-old former guard at Auschwitz goes 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.