A grand jury testimony refers to a testimony by a witness presented before a grand jury. Although the proceedings of a grand jury may be kept secret, the witness can disclose whatever he or she wants to reveal to the members. This exemption was made possible to give the witness an opportunity to refute issues and rumors that may be circulating around concerning his or her testimony.
A witness is usually subpoenaed by a prosecutor to testify before a grand jury. The witness can be anybody and during the trial, he or she is required to answer questions. The person, however, can claim a certain privilege such as the privilege against self-incrimination, marital privilege and lawyer/client privilege.
Additionally under the federal system, while a witness has the right to get a lawyer, he or she could not be accompanied by his legal counsel inside the grand jury room. They can just be allowed to leave the room if necessary to consult with their lawyer.
A grand jury is a kind of jury tasked to determine whether the evidence presented by the prosecutor is sufficient to proceed to a trial. Its main duty is to find out whether there is probably cause through the examination of evidence, issuance of indictments and investigation of the alleged crimes. As such, it is not necessary to hear all the evidence including the conflicting evidence. This type of jury differs from the petit jury which is normally used during a trial.
In the United States, the grand jury possesses special investigative powers that have been in existence since the 1950s. But due to the wide coverage and unrestricted power, this work of the grand jury has been highly criticized.