The following is a transcript from Brian Ross' report on World News Tonight.
The Justice Department formally denies it but law enforcement sources tell ABC News, the congressional bribery investigation has now expanded to include the speaker of the house Dennis Hastert.
(live) Justice Department officials describe the 64-year old Illinois Republican as "very much in the mix" of the corruption investigation.
Something the speaker told ABC News he was unaware of.
Question: You know nothing about it?
Hastert: Somebody leaked it out.
Question: Completely untrue?
Hastert: I know nothing about it.
Part of the investigation is said to involve a letter Hastert wrote three years ago, urging the Secretary of the Interior to block a casino on an Indian reservation that would have competed with other tribes.
The other tribes were represented by convicted lobbyist Jack Abramoff who reportedly has provided details of his dealings with Hastert as part of his plea agreement with the government.
The letter was written shortly after a fund-raiser for Hastert at a restaurant owned by Abramoff. Abramoff and his clients contributed more than $26,000 at the time.
The day Abramoff was indicted, Hastert denied any unlawful connection and said he would donate to charity any campaign contributions he had received from Abramoff or his clients.
This week, following the FBI raid on the office of another congressman under investigation, democrat William Jefferson of Louisiana, Hastert was outspoken in his criticism of the FBI.
Hastert: We are not trying to protect any individual, but we want to protect the prerogatives of the House as far as the constitution..
(live) We're told the investigation is in its very early stages and the allegations may well be unfounded, but its clear the FBI won't hesitate to take the leads to the very top.