Austrian officials plan to exhume a mass grave near a psychiatric hospital that could contain victims of the Nazis' so-called euthanasia program.

Officials in the western Austrian city of Hall told UPI that they will begin digging in March, when the ground thaws. The process could take two years.

The Irish Times reported that construction workers at the hospital, about 6 miles east of Innsbruck, found 220 decomposed bodies while they were excavating the site for a new building.

Though Christian Haring, a director at the hospital, which is still in operation, told the Times it was unclear whether all the bodies were of euthanasia victims, historian Oliver Seifert told UPI that the bodies were buried between 1942 and 1945.

Seifert further told the Guardian in London that the death rate of patients at the hospital spiked toward the end of World War II, even though the hospital was not officially included in the Third Reich’s euthanasia program.

“We know that murder was actively carried out at other psychiatric institutions, by overdosing patients, neglect or undernourishment,” Seifert told the newspaper.

The U.S. Holocaust Memorial Museum says Adolf Hitler’s attending physicians “began to organize a secret killing operation targeting disabled children” in 1939. It was broadened to include disabled adults later that year, the center says.

The program was officially discontinued after an outcry from the public and church officials, but the Times reported that the practice continued unofficially until the war ended.

Experts told the Times that as many as 200,000 people – many of them physically or mentally disabled – are estimated to have been killed.

Hartheim Castle near Linz was occupied Austria’s most notorious euthanasia facility, the site of an estimated 30,000 killings, the newspaper reported.

Scientists exhuming the bodies in Hall will try to determine the identity and cause of death for each victim, and the hospital is asking anyone who believes their relatives are among the victims to come forward.