The affidavit shows that the Federal Bureau of Investigation received information in 2002 that Mr. Nicholson might be trying to get back in touch with his Russian handlers. But while the F.B.I. was pursuing that lead, Mr. Nicholson was able to use his son as a conduit, passing information to him during jailhouse meetings as investigators monitored their contacts. The documents do not say whether lax security at the prison might have contributed to the success of the scheme.

Mr. Nicholson admitted in 1997 that he had received $300,000 from the Russians for the names, identities and missions of numerous C.I.A. employees. He was the C.I.A.’s deputy station chief in Malaysia before returning to agency headquarters in 1994 in a senior counterterrorism post.

In pleading guilty, Mr. Nicholson avoided a possible life sentence and was given 23 years in federal prison. At his sentencing, he told the judge that he had become a Russian spy for the financial benefit of his three children.

Mr. Nicholson’s three children, including his youngest child, Nathan, then 12, went to live with their grandparents in Eugene, Ore., after their father’s imprisonment. Mr. Nicholson asked to be housed near his family and was placed at the medium-security facility in Sheridan, Ore.

Mr. Nicholson’s mail was heavily monitored, and initially, officials said, he sought to use inmates to pass messages to the Russians through their outside mailings. In February 2002, the F.B.I. learned from someone who had been in contact with another prisoner that Mr. Nicholson was trying to use fellow inmates to contact the Russians, according to an affidavit filed in federal court in Oregon by Jared J. Garth, an F.B.I. agent.

Image Nathan Nicholson

That led the F.B.I. to interview a cellmate, who said Mr. Nicholson had confided to him a concern that the C.I.A. information he had would become “stale” and “no longer have value to a foreign government.” He also reportedly said he had a “pension” awaiting him in Russia and planned to repatriate there after he was freed.