What Is Use Immunity? Scope, Limits, and Kastigar Hearings

Use immunity is a federal protection that forces a witness to testify despite the Fifth Amendment, in exchange for a promise that the compelled statements, and anything the government learns because of them, cannot be used against the witness in a criminal case. It is set out in 18 U.S.C. § 6002.¹ The protection runs to the testimony and its fruits, not to the underlying conduct. A witness granted use immunity can still be charged and convicted, as long as the prosecution’s evidence comes entirely from sources unconnected to the compelled testimony.

The Two Layers of Protection

Use immunity works on two levels. The first bars the government from introducing your actual compelled statements as evidence in a criminal case against you. If you testify under an immunity order about your role in a scheme, prosecutors cannot play that testimony at your trial or quote it to a jury.¹

The second layer, derivative use immunity, goes further. It bars the government from following any investigative lead that grew out of your testimony. If you name a co-conspirator or describe a hidden bank account during immunized testimony, prosecutors cannot use that information to track down new evidence against you. Courts have compared this to the “fruit of the poisonous tree” doctrine in Fourth Amendment law: not only is the original testimony off-limits, but anything the government discovers because of it is tainted as well.²

Both layers apply only inside a “criminal case.” Immunized testimony can still appear in civil lawsuits, regulatory proceedings, and administrative hearings.¹

Use Immunity vs. Transactional Immunity

Federal law grants only use immunity. Transactional immunity, which some state statutes still provide, is broader: it bars prosecution for the offenses the testimony covers, regardless of what independent evidence the government might have. Use immunity leaves prosecution on the table so long as every piece of the government’s evidence traces back to a source unconnected to the compelled statements.³

When Congress adopted the current federal framework in 1970, it chose the narrower version. The Supreme Court upheld that choice in Kastigar v. United States, holding that use immunity is coextensive with the Fifth Amendment privilege and therefore sufficient to replace the right to remain silent.⁴ The reasoning rests on the heavy burden the government must later carry to prove its evidence is independent.

What Use Immunity Does Not Cover

Several situations fall outside the protection. Each one tends to surprise witnesses who assume the shield is more complete than it is.

Perjury and False Statements

The statute explicitly carves out prosecutions for perjury, false statements, and failure to comply with the immunity order. If you lie under oath during immunized testimony, the government can use those very statements as the centerpiece of a perjury case against you.¹ The same words that would be entirely off-limits in a prosecution for the underlying crime are fully admissible to prove the lie.

Civil Liability

Because § 6002 bars use of compelled testimony only in a criminal case, immunized statements remain available in civil litigation. A plaintiff in a fraud lawsuit, a regulatory agency pursuing civil penalties, or a party in a contract dispute could potentially introduce your immunized testimony against you.¹ Witnesses facing both criminal exposure and civil claims should weigh this before testifying.

Proffer Agreements

A proffer agreement, sometimes called a “queen for a day” session, is a negotiated contract between prosecutors and a potential cooperator, not a statutory immunity grant. Its terms are usually narrower. The government typically reserves the right to make derivative use of information from a proffer, meaning investigators can follow leads from your statements even though the statements themselves will not come in as direct evidence. Proffer agreements also commonly allow the government to use your statements to impeach you if you testify inconsistently at trial. The full protections of § 6002 apply only when a court issues an order under the statute.

Prosecution After Immunity: The Kastigar Hearing

If prosecutors decide to charge you for conduct you testified about under immunity, they face a demanding pretrial proceeding commonly called a Kastigar hearing. The government must prove that every piece of evidence it intends to use came from a source completely independent of your immunized testimony.⁴ The Supreme Court called this an “affirmative duty.” It is not enough to show that evidence probably came from somewhere else; the government has to prove it did.

Prosecutors prepare for this burden by cataloging and sealing their existing evidence before the witness ever testifies, creating a clear record of what investigators already knew. The Department of Justice also sometimes uses “taint teams” or “filter teams,” groups of attorneys and investigators walled off from the prosecution team, to review materials and prevent immunized testimony from reaching the lawyers working the case.

If the government cannot meet its burden, the charges must be dismissed. The risk becomes acute when immunized testimony is given publicly. In the Iran-Contra investigation, Oliver North’s conviction was reversed on appeal because the prosecution could not sufficiently show that trial witnesses had been uninfluenced by North’s nationally televised immunized testimony before Congress.⁴

Protection Across Federal and State Lines

Because the Fifth Amendment binds both federal and state governments, an immunity grant in one system generally prevents the other from using the compelled testimony. The Supreme Court established this in Murphy v. Waterfront Commission of New York Harbor, reasoning that a witness compelled to testify in state proceedings should not then have that testimony used in a federal prosecution, or vice versa.⁵

The cross-jurisdictional shield has limits. A federal grant does not stop a state from prosecuting you for the same offense; it only stops the state from using your compelled testimony or evidence derived from it. The same holds in reverse. The protection runs to the testimony and its fruits, not to the conduct itself.

Refusing to Testify After an Immunity Order

Once an immunity order issues, the Fifth Amendment is no longer available as a reason to stay silent. The immunity replaces the privilege, because the government can no longer use the testimony against you in a criminal case.¹

A witness who still refuses to answer faces serious consequences. Under 28 U.S.C. § 1826, a federal court can order confinement until the witness complies. The confinement cannot exceed the life of the court proceeding or the term of the grand jury, including extensions, and in no case can it last longer than eighteen months. A confined witness is not entitled to bail if the court finds the appeal is frivolous or filed for delay.⁶

Civil confinement is separate from criminal contempt. A refusal to testify at trial after receiving immunity can be punished summarily as criminal contempt. A refusal before a grand jury must instead be prosecuted through the indirect contempt procedures of Federal Rule of Criminal Procedure 42(b).⁷

1
Office of the Law Revision Counsel. 18 USC 6002 – Immunity Generally
2
United States Department of Justice Archives. Criminal Resource Manual 718 – Derivative Use Immunity
3
United States Department of Justice Archives. Criminal Resource Manual 717 – Transactional Immunity Distinguished
4
Justia U.S. Supreme Court Center. Kastigar v United States, 406 US 441 (1972)
5
Legal Information Institute. United States v Balsys, 523 US 666 (1998)
6
Office of the Law Revision Counsel. 28 USC 1826 – Recalcitrant Witnesses
7
United States Department of Justice Archives. Criminal Resource Manual 780 – Direct Contempt, Witness Refusal to Obey Court Order to Testify at Trial