When the Vatican opened its sealed archives from the World War II-era pontificate of Pius XII in March, the Brown University historian David I. Kertzer was among the first in line.

Like many other scholars, Dr. Kertzer had been eager to mine the papers of a pope — long under consideration for sainthood — whose response to Nazism and the Holocaust has become the target of fierce debate.

Some have cast Pius XII as the pontiff who remained shamefully silent as the Nazis massacred Jews during the war. Others claim that Pius worked behind the scenes to encourage the Roman Catholic Church to save thousands of Jews and other victims of persecution.

Now documents from the archives are beginning to trickle out, offering an early taste of what could emerge from the tens of thousands of papers that scholars had been clamoring to study for decades. Pius XII’s pontificate stretched from 1939 to 1958.

In an article published in The Atlantic on Thursday, Dr. Kertzer revealed previously unpublished documents, including a memorandum advising Pius against making a formal protest when the Gestapo rounded up 1,000 of Rome’s Jews on Oct. 16, 1943, for deportation to the concentration camp in Auschwitz.

Dr. Kertzer also found a trail of documents revealing that Vatican officials directed clerics in France to resist turning over two Jewish boys who had been put in the care of local Catholics and baptized when their parents were killed in Auschwitz — despite rulings by French courts ordering that the boys be given to their aunt.

The church’s defiance of the aunt’s yearslong efforts to reclaim the two boys — Robert and Gérald Finaly — made international headlines at the time, including on the front page of The New York Times. The documents show that Pius was kept informed, even as French nuns and monks were arrested on charges of kidnapping the boys.

“Among historians, my piece I think will be fairly explosive,” said Dr. Kertzer, whose book “The Pope and Mussolini,” about Pius’s predecessor, Pius XI, won the Pulitzer Prize for biography in 2015.

Vatican officials, provided with Dr. Kertzer’s article, did not respond to multiple requests for comment.