From the introduction to The Federal Grand Jury (May 7, 2015 95-1135):
The federal grand jury exists to investigate crimes against the United States and to secure the constitutional right of grand jury indictment. Its responsibilities require broad powers.
As an arm of the U.S. District Court which summons it, upon whose process it relies, and which will receive any indictments it returns, the grand jury’s subject matter and geographical jurisdiction is that of the court to which it is attached.
As a general rule, the law is entitled to everyone’s evidence. Witnesses subpoenaed to appear before the grand jury, therefore, will find little to excuse their appearance. Once before the panel, however, they are entitled to benefit of various constitutional, common law and statutory privileges including the right to withhold self-incriminating testimony and the security of confidentiality of their attorney-client communications. They are not, however, entitled to have an attorney with them in the grand jury room when they testify.
The grand jury conducts its business in secret. Those who attend its sessions other than witnesses may disclose its secrets only when the interests of justice permit.
Unless the independence of the grand jury is overborne, irregularities in the grand jury process ordinarily will not result in dismissal of an indictment, particularly where dismissal is sought after conviction.
The concurrence of the attorney for the government is required for the trial of any indictment voted by the grand jury. In the absence of such an endorsement or when a panel seeks to report, the court enjoys narrowly exercised discretion to dictate expungement or permit distribution of the report.