The FBI and CDC investigation has been hampered by the destruction of a large collection of anthrax spores collected over more than seven decades .
The FBI and CDC investigation has been kept in more than 100 vials at Iowa State University , Ames , Iowa .
The FBI and CDC investigation has been hampered by the destruction of a large collection of anthrax spores collected over more than seven decades and kept in more than 100 vials at Iowa State University , Ames , Iowa .