Washington ? FBI agents searched the congressional office of Rep. William Jefferson of Louisiana on Saturday evening in connection with a public corruption investigation that already has netted two guilty pleas by two associates, authorities said.

The search began at 6:15 p.m. CDT in the Rayburn House Office Building, where Jefferson has an office, said Debra Weierman, an FBI spokeswoman.

It was not clear what agents were looking for and Weierman said she could provide no additional details because the affidavit supporting the search warrant was sealed. But she indicated the search could take several hours.

Jefferson’s lawyer, Robert Trout, said FBI agents refused to allow him or the general counsel of the House of Representatives to witness the search.

FBI agents searched Jefferson’s homes in Washington and New Orleans in August, hauling away boxes and bags from one of the residences.