HARRISBURG -- Michael Manzo, star witness for the prosecution in the so-called Bonusgate corruption scandal, testified before a Harrisburg grand jury for about five hours yesterday.

Questions centered around a scheme in the House Democratic caucus to use taxpayer-funded bonuses as payment for campaign work, said a source close to the investigation. He also was asked which lawmakers and which staffers might have been aware of the plan to use bonuses as an incentive for staffers to work on campaigns.

Mr. Manzo, 39, of Harrisburg, also has been subpoenaed to testify on related matters before a grand jury sitting in Pittsburgh.

Kevin Harley, spokesman for Attorney General Tom Corbett, who is prosecuting the case, would not confirm whether Mr. Manzo provided information to the grand jury, which meets in secret.

Last week during a preliminary hearing for two people already charged in the case, Mr. Manzo testified in open court that his former boss, Majority Leader Bill DeWeese, was aware of a scheme to use taxpayer-funded bonuses as payment for campaign work.

Attorney James Eisenhower, who represents Mr. Manzo, said last week that his client can prove those allegations and that he intends to cooperate with investigators by testifying against any and all of his co-defendants, including former Minority Whip Michael Veon, who represented Beaver Falls for 20 years.

Mr. Manzo is thought to be among the masterminds behind the bonus scheme. As Mr. DeWeese's longtime chief of staff, he was privy to nearly every aspect of House Democrats' legislative and political operations.

He agreed last week to cooperate with prosecutors and plead guilty to felony counts of theft, conspiracy and conflict of interest for his part in using tax dollars to subsidize political work. In exchange, prosecutors agreed to make the court aware of his cooperation before sentencing.

Mr. DeWeese has denied knowledge of the bonus program. He has characterized Mr. Manzo as a disgruntled employee who is desperately fighting to keep himself and his wife, Rachel, also a defendant in the case, out of prison.

Meanwhile, President Judge Richard Lewis of Dauphin County Common Pleas Court has set Jan. 12 as a trial date for those charged in the case.

At least two defendants -- Mr. Manzo and former Veon staffer P.J. Lavelle -- are cooperating in the investigation and have agreed to plead guilty to charges against them, and others could reach plea agreements before trial.

All 12 defendants are connected with the House Democratic caucus. They include state Rep. Sean Ramaley, D-Economy, who is accused of running his 2004 election campaign out of Mr. Veon's district office while he was being paid to provide legal assistance to constituents.

The investigation is continuing and is expected to yield more arrests, Mr. Corbett has said. Agents are investigating all four legislative caucuses.