A New Jersey congressman says the FBI is refusing to release information about the agency?s investigation into the 2001 anthrax attacks at a Hamilton post office.

Representative Rush Holt (D-12th District) says the workers, some of who became sick after being exposed to the deadly virus, want closure and peace of mind that the attacks won?t happen again. Holt says the FBI has denied his requests for a briefing into the investigation several times.

The FBI says it has made significant progress, but has been declining briefings because of concerns that possible leaks would jeopardize the case. It said the investigation it is one of the largest and most complex efforts in its history.

However, Holt says worry over leaks is not a good enough reason to keep the public in the dark.