A Kastigar hearing is a pretrial proceeding in which a federal judge decides whether the government built its criminal case against a defendant without using testimony that defendant was previously compelled to give under a grant of immunity. The name comes from the Supreme Court’s 1972 decision in Kastigar v. United States, which held that when prosecutors force someone to talk by granting immunity, they later carry a heavy burden to show that none of their evidence grew out of those protected statements.1Justia. Kastigar v. United States, 406 U.S. 441 (1972) The hearing exists because the Fifth Amendment right against self-incrimination would mean nothing if the government could compel your testimony and then quietly convict you with it.
What Immunity Actually Gives You
Federal immunity does not shield you from prosecution. Under 18 U.S.C. § 6002, what you get is use and derivative use immunity: the government cannot use your compelled statements, or any evidence it found by following leads from those statements, against you in a criminal case.2Office of the Law Revision Counsel. 18 USC 6002 – Immunity Generally The Supreme Court in Kastigar held this protection is as broad as the Fifth Amendment privilege itself, leaving you in essentially the same position as if you had stayed silent.1Justia. Kastigar v. United States, 406 U.S. 441 (1972)
That is different from transactional immunity, which blocks any prosecution for the underlying crime no matter where the evidence comes from. The federal system does not offer transactional immunity, though some states still do. Under the federal rule, prosecutors remain free to charge you for the same conduct as long as every piece of their case traces back to sources that have nothing to do with your compelled testimony.3Library of Congress. Kastigar v. United States, 406 U.S. 441 (1972) The Kastigar hearing is the mechanism that enforces that line.
What Triggers a Hearing
A hearing becomes necessary when someone who previously gave compelled testimony under immunity is later charged with a crime connected to the subject of that testimony. The defense typically starts the process by filing a motion to suppress evidence or dismiss the indictment.
The threshold for the defendant is low. You do not have to prove the prosecution actually used your immunized statements. Showing that you testified under a grant of immunity about matters connected to the current charges is enough to shift the burden to the government. That makes practical sense: a defendant has no way to know what went on inside the prosecutor’s office or which leads investigators followed. The Supreme Court was explicit that constitutional rights cannot ride on prosecutorial good faith, so it put the whole burden on the government to show its case is clean.1Justia. Kastigar v. United States, 406 U.S. 441 (1972)
What the Government Has to Prove
The prosecution’s obligation is not simply to deny misuse. The Supreme Court described an affirmative duty: for every piece of evidence it plans to introduce, the government must show the evidence came from a legitimate source wholly independent of the compelled statements. The Court called this a “heavy burden,” and it reaches past the evidence itself to bar using immunized testimony as an investigative lead or as a reason to focus on the witness in the first place.1Justia. Kastigar v. United States, 406 U.S. 441 (1972)
The Kastigar opinion did not name a specific evidentiary standard. The D.C. Circuit filled the gap in United States v. North, holding that the prosecution must show by a preponderance of the evidence that no use whatsoever was made of any immunized testimony.4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990) Other circuits have generally followed that approach. The combination of “heavy burden” language with the preponderance standard means judges scrutinize the government’s proof with real skepticism.
Prosecutors who anticipate a Kastigar challenge usually prepare long before the immunized testimony is even given. The Department of Justice instructs them to create a signed, dated memorandum summarizing all existing evidence and its sources before the witness talks, to record the compelled testimony verbatim and store it with controlled access, and to document every new piece of evidence they obtain afterward.5U.S. Department of Justice. Criminal Resource Manual 726 – Steps to Avoid Taint This practice is called “canning”: sealing evidence in a time-stamped container that proves the government already had it. The D.C. Circuit endorsed the term in North.4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990) Investigations involving immunized witnesses also often use taint teams, separate prosecutors and agents walled off from the compelled testimony who work apart from the trial team.
What Happens During the Hearing
The judge conducts the hearing before trial and goes through the government’s evidence piece by piece. For each item or witness the prosecution plans to use, the court examines the paper trail to confirm an independent origin. Investigators may be called to testify about how they obtained particular leads, when they gathered specific evidence, and whether they had any exposure to the immunized statements.
The North court was clear that this inquiry has to be thorough, proceeding “witness-by-witness” and, where needed, “line-by-line and item-by-item.”4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990) The judge then rules on each item. Anything the government cannot trace to an independent source gets suppressed.
What the Judge Can Order if the Government Fails
Remedies work on a sliding scale. If the government cannot establish independence for a specific item of evidence, the judge suppresses that item and trial moves forward without it. If tainted evidence reached the grand jury, the indictment itself must be dismissed. If tainted evidence was introduced at trial, the defendant is entitled to a new trial.4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990)
There is a safety valve. If the government’s failure on a particular item is harmless beyond a reasonable doubt, a conviction can still stand, but the court must put its reasoning in writing and the harmless-error standard is deliberately demanding. A Kastigar violation implicates the Fifth Amendment itself, and courts do not treat these errors lightly.4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990)
How the Oliver North Case Shaped the Hearing
The most instructive Kastigar case in American law is United States v. North, decided by the D.C. Circuit in 1990. Oliver North testified before Congress under a grant of immunity about his role in the Iran-Contra affair, and his testimony was televised nationally. When he was later prosecuted, the question was whether witnesses at his trial had been influenced by watching or reading about his immunized congressional testimony.
The D.C. Circuit held that when a witness uses immunized testimony to refresh memory, organize thoughts, or revise prior statements, that counts as prohibited evidentiary use. It is not some lesser “non-evidentiary” exposure that escapes Kastigar protection. The court vacated North’s convictions and ordered a full Kastigar hearing on remand. For every grand jury and trial witness, the prosecution had to show either that the witness was never exposed to North’s immunized testimony or that the witness’s testimony contained nothing beyond what was already canned before the exposure.4Law Resource. United States v. North, 910 F.2d 843 (D.C. Cir. 1990)
The prosecution could not carry that burden, and the charges against North were dropped. The case stands as a warning about what happens when immunized testimony becomes widely known: the contamination problem can become impossible to clean up. It also expanded Kastigar protection past the government’s own direct use to include the indirect effect of immunized testimony on other witnesses.
Where the Protection Stops
Two limits are worth knowing. First, immunity under 18 U.S.C. § 6002 does not protect you if you lie. The statute explicitly carves out prosecution for perjury, giving a false statement, or failing to comply with the immunity order.2Office of the Law Revision Counsel. 18 USC 6002 – Immunity Generally The government can use your own immunized testimony against you if the charge is lying during that testimony.
Second, a proffer agreement is not the same thing as a formal immunity order and does not trigger a Kastigar hearing in the same way. A formal order under § 6002 is court-issued, compels testimony, and brings full Kastigar protection against both direct and derivative use. A proffer, sometimes called a “Queen for a Day” session, is a voluntary deal between the defense and prosecution governed entirely by its negotiated terms. In a typical proffer the government agrees not to use your statements in its direct case at trial but reserves the right to use anything it finds by following leads from what you said. Most proffer agreements include an explicit Kastigar waiver, meaning you give up the right to challenge derivative use later. The government can also use proffer statements to impeach you if you testify inconsistently, and you can be prosecuted for false statements made during the session. If you are weighing a proffer, understand the gap: you are getting a fraction of the protection that a compelled witness receives under a formal immunity order.