"If you read about the things we did, you'll say, ‘How could anyone do that, burn their fellow Jews?’" wrote Marcel Nadjari in a secret letter he penned while imprisoned at the Auschwitz-Birkenau extermination camp.

Nadjari, a Greek Jewish prisoner, who was given the grisly task of removing dead bodies from Auschwitz’s gas chambers, buried his letter in a forest near the camp before it was liberated in 1945. The document was discovered in 1980, but as Dagmar Breitenbach of Deutsche Welle reports, experts only recently succeeded in deciphering Nadjari’s vital account of Nazi atrocities.

Nadjari was born in 1917 in Thessaloniki. He was deported to Auschwitz in April 1944 and assigned to work as a member of the Sonderkommando—a group of Jewish prisoners forced to assist Nazis in their mass extermination program. At Auschwitz, the Jewish Virtual Library explains, Sonderkommandos greeted prisoners upon their arrival to the camp, telling them that they were being sent to shower, when they were in fact headed to gas chambers. Sonderkommandos removed bodies from the gas chambers, extracted gold teeth from the corpses, removed any valuables, brought corpses to the camp’s crematoria, and threw the ashes into a nearby river.

After writing his letter, Nadjari put the papers inside a thermos, wrapped the thermos in a leather pouch, and buried it. Gizmodo’s George Dvorsky reports that Nadjari hoped someone would find the letter and pass it on to a Greek diplomat, who would in turn hand the letter over to his family in Greece.

A student accidentally uncovered the buried document in 1980, near the crumbling remnants of Auschwitz-Birkenau's crematorium III. The letter was badly preserved and only about 10 percent legible. But using multispectral analysis, the Russian-born historian Pavel Polian has been able to make the document about 85 to 90 percent legible, as he tells Breitenbach of Deutsche Welle.

The account was published in German for the first time this month in the Munich-based Institute of Contemporary History's quarterly magazine. An English translation is underway, and is due to be published next month.

The letter is one of nine separate documents that Poilan has worked on deciphering over the past 10 years. Written by five Sonderkommandos in total, the records were all discovered near Auschwitz. While most of the others were penned in Yiddish, Nadjari’s is the only one that was written in Greek. In his interview with Deutsche Welle, Polian called these letters “the most central documents of the Holocaust." Nadjari’s account, for one, offers remarkable insight into the experiences and psyche of Jewish concentration camp prisoners who were forced to perform unthinkable tasks.

“Our work was to receive [the prisoners] first, most of them did not know the reason,” he writes, according to Dvorsky. “[T]he people I saw when their destiny was sealed, I told the truth, and after they were all naked, they went further into the death chamber, where the Germans had laid pipes on the ceiling to make them think they were preparing the bath, with whips in their hands, the Germans forced them to move closer and closer together, so that as many as possible could fit in, a true Sardinian death, then the doors were hermetically sealed.

“After half an hour, we opened the doors [of the gas chamber], and our work began. We carried the corpses of these innocent women and children to the elevator, which brought them into the room with the ovens, and they put them in there the furnaces, where they were burnt without the use of fuel, because of the fat they have.”

This work weighed heavily on Nadjari. “[M]any times I thought of coming in with them [to the gas chambers],” he wrote. But he was determined to stay alive so he could seek vengeance for his family.

“I wanted to live to avenge the death of Papa and Mama, and that of my beloved little sister, Nelli,” the letter reads.

Nadjari ultimately did survive Auschwitz. He moved back to Greece after the war, and then immigrated to the United States. He died in New York in 1971. He was 54 years old.

In 1947, Nadjari published a memoir about his Holocaust experience. But he does not appear to have told anyone about the letter that he wrote and carefully interred at Auschwitz, a secret testament to the horrors he saw there.