Newly discovered correspondence suggests that Pope Pius 12th had detailed information from a trusted German Jesuit that thousands of Jews and Poles were being gassed each day in German-occupied Poland during World War 2, undercutting the Holy See’s argument that it couldn’t verify diplomatic reports of Nazi atrocities to denounce them.

The documentation from the Vatican archives, published this weekend in the Italian daily Corriere della Sera, is likely to further fuel debate about Pius’ legacy and his now-stalled beatification campaign.

Historians have long been divided about Pius’ record, with supporters insisting he used quiet diplomacy to save Jewish lives while critics say he remained silent as the Holocaust raged.

Corriere reproduced a December 1942 letter from the German Jesuit to Pius’ secretary, which is contained in an upcoming book about the newly opened files of Pius’ pontificate by Giovanni Coco, a researcher and archivist in the Vatican’s Apostolic Archives.

Coco told Corriere that the letter was significant because it represented detailed correspondence about the Nazi extermination of Jews from an informed church source in Germany who was part of the Catholic anti-Hitler resistance that was able to get otherwise secret information to the Vatican.

The letter from the priest, the Rev. Lothar Koenig, to Pius’ secretary, a fellow German Jesuit named the Rev. Robert Leiber, is dated Dec. 14, 1942. Written in German, the letter addresses Leiber as “Dear friend” and goes on to report that the Nazis were killing up to 6,000 Jews and Poles daily from Rava Ruska, a town in prewar Poland that is today located in Ukraine, and transporting them to the Belzec death camp.

According to the Belzec memorial, which opened in 2004, 500,000 Jews perished at the camp. The memorial’s website reports that as many as 3,500 Jews from Rava Ruska were sent to Belzec earlier in 1942, and that from December 7 to 11, the town’s Jewish ghetto was liquidated.

“About 3,000-5,000 people were shot on the spot and 2,000-5,000 people were taken to Beł ec,” it says.

The date of Koenig’s letter is significant because it suggests the correspondence from a trusted fellow Jesuit arrived in Pius’ office in the same three weeks before Christmas 1942 that Pius was receiving multiple diplomatic notes from the British and Polish envoys to the Vatican with reports that up to 1 million Jews had been killed so far in Poland.

While it can’t be certain that Pius saw the letter, Leiber was Pius’ top aide and had served the pope when he was the Vatican’s ambassador to Germany in the 1920s, suggesting a close working relationship, especially on matters related to the Central European country.

According to “The Pope at War” by Pulitzer Prize-winning anthropologist David Kertzer, a top secretariat of state official, Msgr. Domenico Tardini, told the British envoy to the Vatican in mid-December that the pope couldn’t speak out about Nazi atrocities because the Vatican hadn’t been able to verify the information.

“The novelty and importance of this document comes from this fact: that on the Holocaust, there is now the certainty that Pius 12th was receiving from the German Catholic Church exact and detailed news about crimes being perpetrated against Jews,” Coco was quoted by Corriere as saying.

However, he noted that Koenig also urged the Holy See to not make public what he was revealing because he feared for his own life, and those of the resistance sources who had provided the intelligence.