On Wednesday, Abramoff was to plead guilty in Miami to criminal charges stemming from the purchase of SunCruz Casinos in 2000, a case that touches on Bob Ney, an Ohio Republican.
The full extent of the investigation is not yet known, but Justice Department officials said on Tuesday that they intended to make use of e-mails and other material in Abramoff's possession as part of an inquiry that is believed to be focusing on as many as 20 members of Congress and aides.
"The corruption scheme with Mr. Abramoff is very extensive and we will continue to follow it wherever it leads," said Alice Fisher, assistant attorney general and head of the Justice Department's criminal division.
Court papers in Abramoff's case refer to an aide to former Tom DeLay, a former House majority leader who helped stop anti-gambling legislation regarding the Internet.
Abramoff, the papers state, paid the staffer's wife $50,000 from clients that benefited from the actions of the staffer, identified by a person close to the investigation as Tony Rudy, DeLay's former deputy chief of staff.
Assistant Attorney General Alice
Fisher announces the guilty plea
The person spoke on condition of anonymity because the investigation is ongoing.
Rudy did not return a phone call on Tuesday at his lobbying firm.
DeLay, a Republican, voted against his party on the Internet anti-gambling legislation that was designed to make it easier for authorities to stop online gambling sites.
DeLay attorney Richard Cullen said he believed that when the investigation was completed and the truth was known that the Justice Department would conclude that his client, who had risen to House majority leader before stepping down from the post last year, did nothing wrong.
Abramoff pleaded guilty on Tuesday to conspiracy, mail fraud and tax evasion, with his conduct outlined in court papers that refer to "a stream of things of value to public officials in exchange for a series of official acts and influence".
The political ramifications of the Abramoff investigation were apparent, with minority Democrats intending to make ethics a campaign issue in this election year.
House Democratic leader Nancy Pelosi said Abramoff's confession in court was "not a surprise because this Republican Congress is the most corrupt in history, and the American people are paying the price".
"The corruption scheme with Mr. Abramoff is very extensive and we will continue to follow it wherever it leads"
assistant attorney general and head of the Justice Department's criminal division
Some political consultants and analysts are comparing potential damage from the Abramoff investigation to the 1992 House banking scandal that led to the retirement or ouster of 77 lawmakers.
Abramoff's cooperation has made lawmakers nervous.
House Speaker Dennis Hastert, a Republican, became the most recent addition to the roster of politicians announcing plans to donate Abramoff's campaign contributions to charity.
The court papers in the Washington case refer to Ney, saying that regarding SunCruz, the congressman placed a statement drafted by Abramoff partner Michael Scanlon in the Congressional Record.
The statement, the court papers say, was calculated to pressure the owner of SunCruz to sell on terms favourable to Abramoff.
Ney denies wrongdoing, saying that "at the time I dealt with Jack Abramoff, I obviously did not know, and had no way of knowing, the self-serving and fraudulent nature of Abramoff's activities".
Abramoff and his former partner, Adam Kidan, are charged with concocting a false $23 million wire transfer, making it appear they contributed a sizable stake of their own cash into the $147.5 million purchase of cruise ships.
The court papers released on Tuesday in Washington raised questions about Ney's former chief of staff, Neil Volz.
The documents say the ex-staffer contacted the congressman on behalf of an Abramoff client that won a lucrative deal from Ney to improve cell phone reception in House buildings.
Volz contacted his ex-boss within one year of leaving the congressman's staff, the court papers say, a possible violation of federal conflict of interest laws, which impose a one-year lobbying ban.
Volz referred questions to his attorney, who was not immediately available for comment.
Abramoff pleaded guilty to mail
fraud, conspiracy, tax evasion
Abramoff was a well-connected lobbyist able to command almost unimaginable fees: A Louisiana tribe paid Scanlon and him more than $30 million over 26 months. Now facing up to 11 years in prison, Abramoff apologised after pleading guilty.
"Words will not ever be able to express my sorrow and my profound regret for all my actions and mistakes," Abramoff said.
"I hope I can merit forgiveness from the Almighty and those I've wronged or caused to suffer."