privacy interest . . . in keeping secret the fact that they were subjects of a law enforcement investigation,??? as do witnesses and informants); Wichlacz v. U.S. Dep???t of Interior, 938 F. Supp. 325, 333 (E.D. Va. 1996) (???Law enforcement officers, interviewees, suspects, witnesses, and other individuals named in investigatory files all have substantial privacy interests??? because revelation c