WARSAW, Poland (AP) — Polish prosecutors have discontinued an investigation into human skeletons found at a site where German dictator Adolf Hitler and other Nazi leaders spent time during World War II because the advanced state of decay made it impossible to determine the cause of death, a spokesman said Monday.

The remains were found Feb. 24 at Wolf’s Lair, which served as Hitler’s chief headquarters from 1941-44 when the area was part of Germany. The compound of about 200 Nazi bunkers and military barracks hidden in deep woods was the site of the failed assassination attempt on Hitler by Col. Claus Stauffenberg on July 20, 1944. The site is now a tourist attraction.

The spokesman for the prosecutor’s office in nearby Ketrzyn town, Daniel Brodowski, said police officers secured the remains after they were found by a local group, Latebra, which searches for historical objects.