HARRISBURG -- Three investigators and dozens of former campaign operatives are on the witness list for a preliminary hearing tomorrow in a criminal case against 12 state House Democratic employees and elected officials accused in a corruption scandal.

In all, state prosecutors have summoned two dozen witnesses for the hearing that begins Tuesday at the Dauphin County Courthouse. Testimony is expected to last more than a week.

Defendants have the option of waiving the preliminary hearing, but so far only two of the 12 have done so. Mike Manzo, former chief of staff to House Majority leader Bill DeWeese, and his wife, Rachel, waived their hearings.

Dauphin County Common Pleas President Judge Richard A. Lewis on Friday denied a request from three defendants to delay the hearing until after the Nov. 4 election.

Other defendants include state Rep. Sean Ramaley, D-Conway, who is accused of taking a no-work state job while he ran for office, and former House Democratic whip Mike Veon, charged in an alleged plan to distribute taxpayer-funded bonuses to state workers as veiled compensation for campaign work.

The aim of a preliminary hearing is for prosecutors to present enough evidence to corroborate criminal charges and to persuade a judge that a case should go to trial, said Kevin Harley, spokesman for Attorney General Tom Corbett. Defendants could but do not have to present evidence.

Charges against the 12 include theft, criminal conspiracy and conflict of interest for allegedly running a multimillion-dollar scheme to divert public funds to campaigns.

The hearing is expected to make some evidence public for the first time, Mr. Harley has said.