Adding to the FBI's embarrassment over its mishandling of evidence related to the Oklahoma City bombing case, the agency's Baltimore bureau has turned up seven more documents that should have been forwarded to Timothy McVeigh's lawyers, a government official said Monday night, speaking on condition of anonymity.

The seven documents add to the thousands of pages of evidence the FBI failed to turn over to the mass murderer's lawyers — on Thursday it was revealed that 3,135 pages of investigative materials, including interview reports and physical evidence such as photographs, tapes and letters, were withheld.

The FBI requested last Friday that all special agents in charge and assistant directors at all field offices certify that they had turned over all documents that were required to be turned over. That certification has been completed, the source said. The Baltimore documents had already been found before that communication went out.

The discovery of the seven documents was first reported in Tuesday's editions of the Los Angeles Times.

In another development, an anonymous government official disclosed Monday that FBI field offices had been told in December 2000 that some of the bombing records could be discarded, and that those instructions were retracted a month later after archivists discovered that some offices had failed to turn over all their evidence to McVeigh's lawyers.

By January, the source said, archivists became concerned that some documents could be thrown out by mistake. They contacted field offices again, instructing them to send all investigative materials to the Oklahoma City bureau, where the materials were being archived.

Archivists had already discovered that a small percentage of the reports they were receiving had never been turned over to McVeigh's lawyers, the official said.

There was no indication that investigative materials that should have been turned over had been destroyed, but the possibility could not be ruled out, the official said.

"The FBI is tracking down the path of every document that the prosecution turned over to defense attorneys last week," said Mike Kortan, an FBI spokesman.

After last week's disclosure, Attorney General John Ashcroft pushed back McVeigh's execution — originally scheduled for this Wednesday — until June 11 to give the bomber's attorneys time to review the documents. McVeigh's lawyers are poring over the documents; McVeigh is weighing whether the documents provide an opportunity to raise legal challenges to his conviction and execution.

Government prosecutors who worked on the McVeigh case never saw the documents either. They are now sifting through them as well.

Ashcroft said Justice Department attorneys have looked at the papers and don't think they contain anything that creates any doubt about McVeigh's guilt.

A CBS News poll showed that 69 percent of Americans agree with Ashcroft's decision to delay the execution. McVeigh was to be executed for the April 19, 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City that killed 168 people, including 19 children.

With McVeigh's execution set for May, the FBI at the end of last year was doing a routine archiving of all Oklahoma City bombing materials — standard practice in wrapping up a case — when the undisclosed documents were discovered.

Law enforcement officials familiar with the matter have said that the newly disclosed documents are a small percentage of the millions generated during the investigation.

The FBI was moving to a new computer system when investigative documents were being filed electronically and some may never have been downloaded into set of master databases housing all Oklahoma City bombing records, they said. Many of the withheld documents are interview reports about a possible McVeigh accomplice who never materialized, the so-called John Doe No. 2.

McVeigh, who has said there was no John Doe No. 2, reiterated that position in a letter to the Houston Chronicle. His former attorney Stephen Jones has alleged McVeigh was one of a group of conspirators.

"Jones has been thoroughly discredited, so I'm not going to break a sweat refuting his outlandish claims point-by-point," McVeigh wrote in the letter mailed from the federal prison in Terre Haute, Ind.

"Does anyone honestly believe that if there was a John Doe 2 (there is not), that Stephen Jones would still be alive?" McVeigh wrote.

Justice Department Inspector General Glenn Fine has launched an investigation into the belated disclosure of McVeigh documents, said a Justice Department official. Ashcroft requested the investigation on Friday.

The Associated Press contributed to this report.