The documents, part of what is known as the "Panetta review," were compiled by CIA officers who were sifting through the millions of pages being turned over to the Senate as part of the Senate investigation into the CIA's brutal treatment of al-Qaida detainees after the September 11, 2001 attacks.
The board, led by former Democratic Senator Evan Bayh, found fault with some of the findings by the CIA's inspector general, who said in July that five CIA employees "improperly accessed" a Senate portion of a shared computer network.
The Bayh-led board said the five CIA employees did not deserve to be punished.
"They acted reasonably under the complex and unprecedented circumstances involved in investigating a potential security breach in the highly classified shared computer network," the board said in a statement.
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The CIA accessed five emails of Senate aides, but the board concluded the access was a mistake and did not reflect malfeasance or bad faith.
The aides took the documents out of a Virginia facility run by the CIA which had been set up to allow Senate investigators to review classified material.
The documents were redacted and taken to the Senate's secure facility in the Hart building near the Capitol. They were not used in the Senate report on CIA interrogations, which was harshly critical of the agency.