United States v. Procter & Gamble Co., 356 U.S. 677, 681, 78 S.Ct. 983, 986, 2 L.Ed.2d 1077 (1958) held that there is a "long-established policy that maintains the secrecy of the grand jury proceedings in the federal courts." This public policy serves "to encourage all witnesses to step forward and testify freely without fear of retaliation." Id. at 682, 78 S.Ct. at 986. Grand jury secrecy is maintained because "the grand jury as a public institution serving the community might suffer if those testifying today knew that the secrecy of their testimony would be lifted tomorrow." Id. To preserve the institution, the secrecy is not broken "except where there is a compelling necessity" for the material. Such necessity "must be shown with particularity." Id. In Procter & Gamble, relevancy and usefulness to another case were not enough to require disclosure of grand jury materials. The party seeking disclosure had to provide "proof that without the transcript a defense would be greatly prejudiced or that without reference to it an injustice would be done." Id. District courts that contemplate ordering disclosure must consider the "possible effect upon the functioning of future grand juries." Id. Although "as the considerations justifying secrecy become less relevant, a party asserting a need for grand jury transcripts will have a lesser burden in showing justification" for their disclosure, the interests in secrecy are "not eliminated merely because the grand jury has ended its activities." Id. at 222-23, 99 S.Ct. at 1674-75. In determining whether the party requesting disclosure has met his burden, the district court has "substantial discretion." Id.