Long-secret CIA files on Nazi war criminals reveal for the first time how the United States retained the one-time Nazis as part of its Cold War intelligence operations against the Soviet Union.

The files were released Friday by the Interagency Working Group, created by Congress in 1998 to declassify World War II-era documents.

"The documents prove that named Nazi war criminals were retained in the hopes they would provide intelligence to help the U.S. in the Cold War," IWG member Thomas Baer told Fox News.

In a rush to gather any information the Germans had about the Soviet Union following World War II, the U.S. Army hired the Nazi war criminals to "tell what they knew" in exchange for being let off for their crimes, the documents show.

CIA expert Robert Jervis, a professor at Columbia University, told Fox News the documents highlight the urgency of the times.

"We were desperate for information about East Germany, Eastern Europe and the Soviet Union. Almost anyone who looked like they had decent information was tempting," Jervis said.

But the decision to use the Nazis turned out to be a disaster.

After working for the U.S. Army, some of the Nazis went to work in 1949 for Gen. Reinhard Gehlen, who headed the intelligence arm of the new West German government. According to the documents, some of the Nazis wound up working for the Soviet Union, which succeeded in getting the Nazis to pass on Western secrets.

"The files show that high-ranking Nazi Wilhelm Krichbaum hired three former Nazi colleagues who turned out to be Soviet agents in disguise," Baer told Fox News.

Krichbaum, arrested by the Army in l945, was head of a Nazi group called the Geheime Feldpolizei, which carried out "with energy and dispatch" atrocities against civilians in Europe.

After the war, while in the West German intelligence organization, Krichbaum actively sought to recruit ex-SS, SD and Gestapo men. He succeeded, but he also hired Soviet counterspies who compromised the entire operation.

In 1961, the West German Government indicted the counterspies, exposing the penetration of its intelligence operation to public view. Although Western intelligence was clearly compromised, Jervis said, "It’s not fully clear who helped who the most." Counterspies were common at that time, Jervis explained, adding, "Since the Russian records are still not fully available, there is still so much we have to learn."

"When you lie down with dogs, you get up with fleas," said Baer. "The lesson is that America had no business using this slime, and the results prove it."

Baer credits CIA director George Tenet with "extraordinary cooperation" under the IWG legislation.

"Look, the CIA is an organization whose activities are and should be secret," Baer said. "To make their files public with few redactions as required by law is a seismic event for them."

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