ision is the existence of a relevant statute and the inclusion of withheld material within the statute's coverage. Ass'n of Retired R.R. Workers v. U.S. R.R. Retirement Bd., 830 F.2d 331, 336 (D.C. Cir. 1987). In invoking Exemption 3, the FBI relies on three statutes that preclude disclosure of the documents sought by