e an obvious 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. Dept 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 interestsbecause revelation co