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b6 b7C be March 19, 2007 The Honorable Robert S. Mueller, fi Director Federa) Bureau of Investigation 935 Pennsylvania Avenue, NW. ; ALL INFORMATION CONTAIWED Washington, D.C. 20535 HERETN I$ UWCLASSIFIED DATE 06-11-2007 BY 65179 DMHVKSR/IW | Dear Director Mueller: lam writing today in response to the Justice Department [Inspector General’s March 9, 2007, report entitled “A Review of the Federal Bureau of Investigation’s Use of National Security Letters” and in anticipation of the Inspector General's testimony next week before the Judiciary Committee. In my view, the most troubling section of the report begins on p. 86 and is entitled “Using ‘Exigent Letters’ rather than ECPA National Secunty Letters.” That section describes how an FBI headquarters division known as the Communications Analysis Unit (“CAU") obtained information on about 3,000 telephone numbers by issuing 739 so-called “exigent letters.” In exercising our oversight responsibilities, it is critical for the Judiciary Committee to obtain a fuller understanding of who at the FBI knew what about these exigent letters, and when they knew it. Therefore, in order to prepare for next week’s hearing, please provide copies of any and ali unclassified e-mails related to the exigent letters issued by CAU. If you have any questions about this request, please contac ___} (202) 224 of all correspondence in reply should be sent ehectremeally in or Via facsimile to “Charles E. Grassley U.S. Senator ce: Senator Patrick Leahy, Chairman Committee on the Judiciary Senator Arlen Specter, Ranking Member Committee on the Judiciary