The one-time top aide to former Rep. Curt Weldon pleaded guilty in federal court Friday to a conspiracy charge as part of a plea agreement.

Russell James Caso Jr., 34, who was chief of staff for the Pennsylvania Republican, admitted he intentionally did not report to the House income his wife made for doing work for a nonprofit company tied to Weldon.

Assistant U.S. Attorney Howard Sklamberg told U.S. District Judge Henry H. Kennedy Jr. that Caso has agreed to cooperate with prosecutors in an investigation. Outside court, Sklamberg was asked after the hearing whether that probe involved Weldon. The prosecutor said he could not discuss the case.

Weldon has not been charged. He used to represent the Philadelphia-area, speaks Russian and led congressional trips abroad before his loss last year.

He served on the governing body of the nonprofit, which sought to help U.S. businesses operate in Russia and facilitate the flow of trade between the countries, records show.

At Weldon's direction, Caso organized meetings in which Weldon and Caso made presentations to high-level officials in the departments of State and Energy and the National Security Council seeking money for the proposals that Caso's wife, Sherrill Caso, had worked on, according to court records.

One proposal sought to facilitate cooperation for joint missile activities and the other sought to reduce the risk of proliferation of biological and chemical weapons from Russia to rogue nations, records show.

Court records indicate that Caso's wife did "little work" for $17,500 she received from the company, but that she received $1,500 for editing documents for the firm that were part of the proposals presented to the officials.

Caso could face up to five years in prison. His next court date is May 23.

Caso was Weldon's top aide in 2005 and 2006. He was named a vice president this year at Avineon Inc., a technology company that has contracts with the government.

Caso's lawyer, Kelly Kramer, declined comment after the hearing.

Weldon spent 20 years in Congress before losing to Rep. Joe Sestak, D-Pa. Weldon was vice chairman of the House Armed Services Committee at the time of his loss.

Three weeks before Election Day last year, the FBI raided the homes of Weldon's daughter, Karen Weldon, and her business partner, Charles P. Sexton Jr., as well as other locations. Weldon has denied any wrongdoing.

A phone message left with Weldon's defense lawyer, William Winning, was not immediately returned on Friday.