One escaped Jew told U.S. agents in August 1942 of Adolf Hitler's "program of destroying all European Jewry," according to USA Today.
That and other early signs of the Holocaust were found when a National Archives panel looking at what American spy agencies knew about World War II atrocities delved into the records of the FBI, the CIA and its predecessor the Office of Strategic Services.
"The question of why the U.S. or the West didn't do more is a question that troubles every generation," Richard Breitman, an American University professor and one of the researchers, told CBSNews.com.
Some feel the U.S. strategy of simply trying to win the war quickly was the best course. Others feel more could have been done to stop the slaughter of Jews and others in death camps.
"We wanted to see if intelligence agencies had more information than the rest of the government or the media generally," Breitman said.
That question led Breitman and fellow researchers through 240,000 pages of documents at the National Archives, including intelligence officers' interviews with Jews who left Axis countries in 1941 and 1942.
USA Today quotes one document in which an émigré from Prague, Joseph Goldschmied, tells U.S. agents he saw Jews sent to the Theresienstadt detention camp.
"If Hitler remains true to his program of destroying all European Jewry — he will have achieved this goal soon," Goldschmied said.
"It looks pretty clear, based on the sources that the OSS had, that they had a good amount of information by the middle of 1942," Breitman said. But it was another six months before the rest of the U.S. establishment began to realize what was happening in Germany and occupied Europe.
"I don't think that (intelligence) information quite got to the policymakers" in mid-1942, Breitman said, so allied leaders "never had the opportunity" to make changes in war strategy.
The archives research also revealed that the CIA recruited Germans who may have committed war crimes, while the CIA, FBI and Army protected other Nazis.
Government historian Norman J.W. Goda, one of Breitman's collaborators, said the FBI "did not dig deep for the truth" on such people because it wanted them on America's side in the Cold War with the communist-controlled Soviet Union.
Also in the papers was a German translator's description of a July 20, 1944 tea party hosted by Hitler and attended by Benito Mussolini. Hitler had just escaped an assassination attempt, and was "in a fit of frenzy" with "foam on his lips," saying he doubted "the German people are worthy of my great ideas," the description read, according to USA Today.
One possible reason that U.S. intelligence was slow to recognize the seriousness of the Nazi policy on Jews was that "the U.S. was relatively new at the intelligence business," Breitman said.
British spies, working in agencies launched around World War I, were hearing radio reports about Nazi atrocities. But centralized U.S. intelligence work really didn't begin until the establishment of the Coordinator of Information in 1941, followed by the OSS in 1942.
The government saw Nazi sympathizers as useful in countering any pro-communist leanings in immigrant communities in the United States, and the CIA and other agencies sometimes thwarted immigration authorities from beginning deportation proceedings, the records show.
In the thousands of files released, the CIA is also shown seeking the Immigration and Naturalization Service's help in easing travel in and out of America for Mykola Lebed, a Ukrainian accused of aiding German storm troopers in brutal suppression of local resistance during World War II.
The INS found "some basis for at least some of these allegations," according to a 1953 letter from the agency seeking direction from the Justice Department. If they were true, the agency said, Lebed should be deported.
But INS called off its investigation of Lebed at the CIA's request, even while declining at that time to give him freedom to leave and return to the United States at will.
"I do not feel that we are in any position to give such assurance, since there is a strong likelihood that subject is inadmissible under the immigration laws," the INS commissioner wrote.
The records also describe the case of Viorel Trifa, an alleged student leader in Romania's fascist Iron Guard movement who became bishop of the Romanian Orthodox Church in the United States and once led prayers in Congress.
In a 1953 document, the CIA cited evidence that he had been a "moving spirit" in the 1941 Iron Guard rebellion and pointed to his manifesto openly calling for the pro-Nazi movement to prevail. Trifa denied being part of the group while acknowledging he was close to its leaders.
The FBI understood Trifa's background, Goda said, but FBI Director J. Edgar Hoover considered him a "very desirable part of the landscape during the Cold War.
Trifa was stripped of his U.S. citizenship and deported in 1984, and the Portuguese government took him, Goda said.