Documents with potential evidence were shredded in at least two instances since the government made public its investigation into defense contracts, federal court papers show.

The papers filed by the U.S. attorney's office in Brooklyn late Wednesday were in response to a request by the newspaper Newsday to unseal various search warrants and affadavits in the investigation.Joseph Aronica, assistant U.S. attorney for the Eastern District of Virginia, revealed in the court papers, "In the short time since the execution of the search warrants became public, the government has already become aware of several incidents of destruction of documents related to this case."

Aronica added, "The government has become aware of two incidents of document destruction by persons who are implicated in the investigation, which in two separate instances required the securing of premises to prevent further destruction."

The U.S. attorney's office maintained that unsealing the search warrant for the Hazeltine Corp., a defense firm with offices in Arlington, Va., and Greenlawn, N.Y., "could reveal the identity of a person who has been cooperating with the government's investigation."

Releasing all information sought by Newsday "at the earliest stages of this investigation would send a particularly unfortunate message to witnesses whose cooperation the government is currently seeking," federal prosecutors argued.

Furthermore, they said, the seal "is not a permanent one; the investigation is entering an important new preliminary phase."

Much of the information in the sealed court papers, particularly electronic surveillance materials, has not been made public. But the government said it was willing to release several documents, including the front page of both the search warrant and the warrant application and affidavit for Hazeltine Corp.