ROME >> A letter found among the private papers of Pope Pius XII suggests that the Holy See was told in 1942 that up to 6,000 people, “above all Poles and Jews,” were being killed in furnaces every day at Belzec, a Nazi death camp in Poland.

Although news of the atrocities being perpetrated by Adolf Hitler was already reaching Pius’ ears, this information was especially important because it came from a trusted church source based in Germany, said Giovanni Coco, a Vatican archivist who discovered the letter. The source was “in the heart of the enemy territory,” Coco said Saturday.

The document, which was made public this weekend by Milan newspaper Corriere della Sera, adds to the evidence that some scholars say shows Pius knew about the Holocaust as it happened. Some scholars say Pius did not want to confront or offend Hitler because he feared communism, believed that the Axis powers would win the war and wanted to avoid alienating millions of German and Nazi-sympathizing Catholics.

Other historians insist that Pius remained silent publicly because he was surreptitiously arranging for — or at least allowing — local Catholics to aid and save Jews from the Nazis, and he also feared that the Nazis might come after Catholics.

It is one of the most revealing documents to have emerged since Pope Francis ordered the archives of Pius opened in 2019, saying that “the church is not afraid of history.”

Coco said he could not be 100% sure that Pius saw the letter, but he was “99% sure” because it was given to the pope’s personal secretary, his “right-hand man.” The secretary would have referred the information to the pope, “if he didn’t show him the documents directly,” Coco said.

Since 2020, scholars have been mining the documents covering Pius’ papacy, which lasted from 1939 to 1958, seeking to better understand the Vatican’s response to Nazism and the Holocaust, as well as the controversial legacy of Pius, who was publicly silent as millions of Jews were killed.

Addressed to Pius’ secretary, the Rev. Robert Leiber, the letter was written by a German Jesuit priest, the Rev. Lothar Koenig, who was a member of a German resistance movement. In the letter, which was dated Dec. 14, 1942, Koenig sought to tell the Vatican about “the state of the persecution of the church in Germany, above all,” said Coco, who has been cataloging Pius’ personal papers at the Vatican.

The letter included an appendix with the number of priests imprisoned at the Dachau concentration camp near Munich; mentioned the Auschwitz death camp in Poland in a reference to another, as yet undiscovered report; and told of the thousands of Poles and Jews being murdered by the Nazis at Belzec.

Michele Sarfatti, of the Contemporary Jewish Documentation Center in Milan, who has also been studying the Pius archives, said the letter was important because it had been found in Pius’ personal papers, which meant the pontiff had kept it “and presumably read it.” From a historiographical point of view, it was an indication “that the pope was aware of what was going on” and of the enormity of what was happening in various camps, Sarfatti said.

The Vatican did not respond to requests for comment.

Coco said he believed that Pius was afraid to speak out against Hitler because the Nazis would target Catholics in retaliation.

“There was concern about what could happen to Catholics in Poland, in Eastern Europe, in the Third Reich, all those territories under Nazi control where it was difficult for the church to intervene,” he said.

The letter entreats the Vatican to be cautious in making the information it provides known “because if it emerged that it came from the German church, the persecution would become fiercer in Germany than it already was,” Coco said.

Sarfatti, whose most recent research focuses on documentation from 1942, identified by some scholars as “the bloodiest year of the Holocaust,” said the Holy See received reports that year about the atrocities from innumerable sources: priests returning to the Vatican from trips, local clergy, papal nuncios, politicians from occupied countries, citizens, Jewish groups and rabbis.

“Many people were writing to the Holy See describing what was happening,” Sarfatti said.

At the beginning of 1942, few people, including Jews, understood that Hitler wanted to exterminate the Jews. But as the year progressed, “there was a growing association between the words ‘Jew’ and ‘death’ in these reports — that in itself should have given a sense of what was going on,” he said.

Sarfatti, who in the Vatican Apostolic Archive found two documents referring to gas chambers, said the letter was proof “that we can add to others.”

David Kertzer, a Brown University professor who has been working in the archives, said the document was “more detail” about “reports that the pope is getting in the summer of 1942 about the mass murder of the Jews” from various sources, which are discussed in his book on Pius, “The Pope at War.”

Coco said he believed that the letter he found was part of a “much longer correspondence” that preceded and continued after December 1942. Pius felt “particularly close to” German Jesuits, Kertzer said, Pius’ secretary being a major example.

“There would be no more believable source for the pope about what was going on there than from a German Jesuit,” Kertzer said.

The letter will be published next week in a book by Coco about his research on Pius’ personal papers. He said the papers were in disarray when he first started studying them in 2019, and he found the letter about a year ago. It took time to track down the author: The letter is signed, “Your Lothar,” and it is addressed, “Dear Friend,” Coco said.

“Organizing the papers,” to better understand them, “has been very complicated,” he said.

This article originally appeared in The New York Times.

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