406 U.S. 441 (1972), argued 11 Jan. 1972, decided 22 May 1972 by vote of 5 to 2; Powell for the Court, Douglas and Marshall in dissent, Brennan and Rehnquist not participating. In Kastigar the Court for the first time squarely confronted the question of whether witnesses can be compelled to testify before grand juries under a grant of use immunity. In 1970, Congress had substituted use for transactional immunity in the federal immunity statute. Use immunity prevents the government from using compelled testimony or any information derived from such testimony against the witness in a subsequent criminal prosecution. It is not as broad as transactional immunity, which prevents any prosecution of a witness for offenses related to the compelled testimony. Kastigar argued that the Fifth Amendment privilege against self-incrimination prohibits the compulsion of testimony under a grant of use immunity but instead requires transactional immunity at the very least.
In rejecting that argument, the Court first noted that the power to compel testimony in court or before a grand jury is firmly established and essential to the effective funcioning of government. That power, however, is not absolute but is limited by the Fifth Amendment privilege against self-incrimination. The Fifth Amendment protects a person from being forced to give testimony that could be used against him or her in a subsequent criminal prosecution. Use immunity, the Court concluded, is compatible with the Fifth Amendment because it ensures that the compelled testimony cannot lead to prosecution. In a subsequent prosecution, an affirmative duty is placed on the government to prove that evidence it seeks to use is derived from a source wholly independent of the compelled testimony. As a result, use immunity removes the danger that testimony will be used against the witness and, thus, does not violate the privilege against self-incrimination.