At a news conference releasing some 400,000 pages of newly declassified documents at the National Archives, historians said Western officials might have been able to warn Jews in Rome that they were about to be rounded up and deported.
Some 1,000 Roman Jews died in Auschwitz, reports CBS News Correspondent Eric Engberg. It is clear now that they could have been warned. U.S. President Franklin Roosevelt and British Prime Minister Winston Churchill, faced with the problems of running the war, apparently never discussed that.
In October 1943, American and British forces landed in Italy and were moving in on to Rome.
In coded radio messages to SS leaders in Rome, Hitler ordered the slaughter.
A message dated October 6, 1943, read: "...take to Northern Italy the 8,000 Jews living in Rome. They are to be liquidated."
Another, dated October 11, ordered, "...the immediate and thorough eradication of the Jews in Italy."
The orders were intercepted by the British and shared with the Americans in London at the time.
Using the super-secret code breaking methods known as "Ultra," the British were tapping into German message traffic, and passing it to the Office of Strategic Services (OSS), the World War II forerunner to the CIA.
Some of the messages went right to President Roosevelt.
Historian Timothy Naftali says, "There was a fear that if you let the Germans know you could read their mail, they would tighten their cipher security and all of their communications would become more difficult to decipher."
The 1998 War Crimes Disclosure Act seeks to make public intelligence information that countries often refused to relinquish even years after the war.
Michale Kurtz, of the National Archives says: "These records are filled with what are called sources and methods: the names of agents and intelligence gathering methods. (They are) also filled with foreign government information."
Some 400,000 pages were de-classified on Monday, and more are coming, almost surely revealing more controversial decisions by the leaders who fought Hitler.
The declassified documents from the OSS also included conversations among German POWs secretly recorded by the British and information gathered by the OSS using an anti-Nazi German informant.
"The release...raises the historical question once again of what Allied governments knew about the Holocaust during World War II and might have been done with information they possessed," said historian Richard Breitman in a report he co-authored for the U.S. government's Nazi War Criminals Records Interagency Working Group.
Naftali, the co-author of the report, said perhaps Churchill or Roosevelt should have made a statement warning the Jews.
"It is clar that had a statement been made on the radio to the effect that Allied forces feared for the safety of Romans, and particularly the Jews of Rome, this might well have had an effect on decisions made by people to get out," Naftali said.
"I find it disheartening that there was no more use of some of this information at the time," said Breitman.
But Naftali also warned against a "rush to conclusions." He and others said it is unclear in hindsight whether taking action on the information would have compromised British intelligence gathering.
Others said it was unclear whether Jews could have acted on the information had they received it.
The interagency working group was established in January 1999 to coordinate a large-scale effort by U.S. federal agencies to find, declassify and release U.S. records relating to Germany's Nazi regime.
Federal agencies have resisted opening their files for half a century, saying national security was at stake. Supporters say the panel's work provides an insight into how U.S. intelligence agencies and others used Nazi war criminals in the Cold War years.
Historians said this was the most significant finding by the panel, which has released more than one million pages of documents gathered from the Department of Defense, the OSS, Justice, State, FBI and other agencies.
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