The anthrax in the letters sent to government and media offices in Washington and New York cannot be definitively tied to the anthrax in the possession of a Fort Detrick researcher, according to a new report released Tuesday by the National Research Council.

A committee of the NRC reviewed the scientific procedures used by the FBI during its investigation of the anthrax attacks that killed five people and sickened 17 over a period of weeks after the Sept. 11, 2001 attack.