Polish authorities have reopened investigations into crimes committed at Auschwitz and other concentration camps in the country during World War Two, in a final attempt to track down any remaining Nazi perpetrators.

The announcement was made Thursday by the Institute of National Remembrance, the state body charged with investigating wartime crimes. If new perpetrators are discovered, they could be charged for their crimes and face trials.

Investigators are hoping to interview some of the estimated 500 death camp survivors who are still alive. Between 1940 and 1945, as many as 1.5 million people, most of them Jews, were murdered at the Auschwitz-Birkenau camp. Another goal of the probe is to get a final account of the number of people who were killed at the camps.

Many people who worked at the camps were captured and punished after World War Two. But the trials stopped, and some of those jailed for crimes were released in 1956, when an official amnesty was declared.

The new investigation is an attempt to finish a 1970s probe by communist authorities that ended in the 1980s without any indictments. Poland ran into problems questioning witnesses and perpetrators outside the country because it was cut off behind the so-called “Iron Curtain,” which for decades divided eastern and western Europe.