Kastigar Motions and Hearings in Federal Court

What a Kastigar Motion Is and Its Legal Basis

A Kastigar motion is a federal criminal-defense request that follows one specific event: the government compelled a person to testify or produce information after that person invoked the Fifth Amendment privilege against self-incrimination. A witness cannot be jailed for silence and, at the same time, be stripped of the privilege, so federal law offers a trade. A court may order the witness to speak, but 18 U.S.C. § 6002 then bars the government from using that compelled testimony, or anything derived from it, against the witness in any later criminal case.

The motion takes its name from Kastigar v. United States, 406 U.S. 441 (1972). There, the Supreme Court upheld the immunity statute and held that use-and-derivative-use immunity is coextensive with the constitutional privilege. Id. at 453. If the immunity the witness received is the constitutional equal of remaining silent, then a later prosecution must proceed as though the witness had never spoken.

In practice, a Kastigar motion asks the district court to hold the government to that promise. It requires prosecutors to come forward and show, on the record, that each item of evidence they intend to use has a legitimate origin wholly independent of the immunized statements. The evidentiary hearing that follows is commonly called a taint hearing or, simply, a Kastigar hearing.

The stakes are high because immunized testimony often comes from grand-jury appearances, regulatory investigations, or cooperation sessions. The Kastigar framework is what keeps those compelled words from quietly powering a later prosecution of the same person.

Use, Derivative-Use, and Transactional Immunity

Immunity comes in different strengths, and the difference decides how much protection a witness actually has. Federal courts recognize three principal forms.

Use immunity

Promises only that the literal words of the compelled testimony will not be introduced against the witness.

Derivative-use immunity

Adds a promise that no evidence or investigative lead obtained because of the testimony will be used either.

Transactional immunity

Goes further still and bars prosecution altogether for the offenses the testimony concerned.

The statute at the center of a Kastigar motion, 18 U.S.C. § 6002, supplies use-and-derivative-use immunity. In Kastigar, the Supreme Court rejected the argument that the Constitution demands transactional immunity, holding that use-and-derivative-use protection alone is enough to supplant the privilege because it leaves the witness and the government in substantially the same position as if the witness had stayed silent. 406 U.S. at 462. Bare use immunity, standing alone, would not satisfy the Fifth Amendment, because it would still let investigators follow the leads the testimony provided.

Identifying which type applies is the first analytical step in any Kastigar dispute, because the label controls both the scope of the protection and the size of the burden the government must later shoulder.

The Government's Independent-Source Burden

The defining feature of the Kastigar framework is where it places the burden of proof. Ordinarily a defendant who wants evidence excluded must prove that something went wrong. The immunity setting flips that arrangement.

As the Supreme Court put it, once a person shows he testified under a grant of immunity, that showing alone shifts to the government the heavy burden of proving that all of the evidence it proposes to use was derived from legitimate, independent sources. Kastigar, 406 U.S. at 461-62. The Court described this as an affirmative duty that is not satisfied by merely denying taint; the prosecution must affirmatively prove that its evidence comes from a source wholly independent of the compelled testimony. The rule traces back to Murphy v. Waterfront Commission, 378 U.S. 52 (1964), which first held that once a witness shows immunized testimony on related matters, the authorities must establish an independent, legitimate source for their evidence.

In the Fifth Circuit, which governs federal prosecutions in North and East Texas, the government must carry this burden by a preponderance of the evidence. United States v. Cantu, 185 F.3d 298, 301 (5th Cir. 1999). The obligation is comprehensive. It reaches not only exhibits and physical evidence but also the testimony of witnesses, the leads that steered the investigation, the decision to focus on the defendant at all, and the evidence presented to the grand jury.

Practically, prosecutors who are exposed to immunized testimony often build a documented, timestamped record of what they knew, and from where, before the testimony existed. When the government cannot trace an item of proof to a pre-existing, independent origin, that item is vulnerable, and the taint can spread to whatever grew out of it.

When a Kastigar Hearing Is Triggered

A Kastigar hearing is not automatic. It is triggered when two things line up: a person gave testimony or information under compulsion and a grant of immunity, and the government later pursues a criminal prosecution against that same person on related matters.

The defendant carries a modest threshold burden to open the door. Under Kastigar and Murphy, the defendant need only show that he testified under immunity about matters related to the prosecution. 406 U.S. at 461-62. That showing is usually straightforward, because it rests on records of the immunity order and the transcript of the compelled session. Once made, the burden shifts, and the government must justify its evidence.

Several recurring situations set the stage for a hearing:

• A witness testified before a federal grand jury under a Section 6003 immunity order and is later indicted.
• A person gave compelled statements in a parallel regulatory, civil, or congressional proceeding that the criminal prosecutors could have seen.
• A defendant cooperated under a proffer or plea-related agreement, then the deal collapsed and charges followed.
• A state grant of immunity precedes a federal prosecution, or the reverse, implicating the cross-sovereign rule of Murphy.

Timing matters. The motion is ordinarily raised before trial so the court can screen the government's proof in advance, but exposure discovered during or after trial can support a post-trial Kastigar inquiry as well. Because the grand jury that returned the indictment may itself have heard tainted evidence, the hearing sometimes examines not just the trial evidence but the origins of the charging decision.

The Hubbell Act-of-Production Dimension

Immunity problems are not limited to spoken testimony. The Supreme Court's decision in United States v. Hubbell, 530 U.S. 27 (2000), extended the Kastigar analysis to the act of producing documents.

The idea is that handing over records in response to a subpoena can itself be a form of testimony. By producing documents, a person implicitly represents that the papers exist, that they were in his possession or control, and that they are authentic. 530 U.S. at 36. When the government compels that production under a grant of immunity, it may not make derivative use of the testimonial act to build its case.

In Hubbell, prosecutors used an immunized document production to assemble a new tax and fraud indictment. The Court held that the government could not do so without showing a prior, independent source for its knowledge of the documents. Because the prosecution had not shown that it knew of the existence or location of the produced records beforehand, the so-called foregone-conclusion doctrine did not apply, and the indictment could not stand. 530 U.S. at 44-45.

For defense purposes, the act-of-production dimension broadens the reach of a Kastigar motion. A defendant who was compelled to gather and produce business records, devices, or files under immunity can argue that the government's later use of the contents, or of anything learned by reviewing them, must survive the same independent-source test that applies to compelled words.

The doctrine has limits. It does not shield the pre-existing contents of voluntarily created documents, and it does not apply where the government can independently establish the existence, possession, and authenticity of the records. But where compelled production is the reason the government found or understood key evidence, Hubbell brings that evidence within the Kastigar analysis.

Proffer and Queen-for-a-Day Statement Limits

Many people first give incriminating information not before a grand jury but in a proffer session, sometimes called a queen-for-a-day meeting. In these sessions a person sits down with prosecutors and agents, usually with counsel present, to preview what he knows in the hope of a cooperation deal or a favorable resolution.

Proffer protection is different from statutory immunity, and the difference is critical. A statutory immunity order under 18 U.S.C. § 6002 delivers the full use-and-derivative-use protection that Kastigar guarantees. A proffer agreement, by contrast, is a contract, and its protection is only as broad as its written terms.

Typical proffer letters promise that the government will not use the person's proffer statements directly in its case-in-chief, but they frequently reserve the right to make derivative use of the information, and to use the statements for cross-examination or rebuttal if the defense offers contradictory evidence at trial. That reservation is the very thing full statutory immunity forbids.

The practical lesson is that not every cooperation session generates Kastigar protection. When it does, because a formal immunity order issued or the agreement's language tracks the statute, a defendant can invoke the full independent-source burden. When it does not, the analysis becomes a question of contract interpretation and voluntariness. Reviewing the exact instrument that authorized the statements is therefore an essential early step, and it explains why the wording of a proffer or immunity order should be examined closely before anyone speaks.

How a Kastigar Hearing Is Litigated

A Kastigar hearing is an evidentiary proceeding, not a paper exercise. Although the details vary by district and judge, the litigation generally moves through recognizable stages.

1. The motion and threshold showing. The defense files a motion establishing that the defendant testified or produced information under immunity about matters related to the charges, which shifts the burden to the government.
2. Disclosure of the immunized material. Courts in the Fifth Circuit have required that the district judge have the defendant's immunized statements in order to decide the issue fairly, and that requirement extends to what was presented to the grand jury and at trial. Cantu, 185 F.3d at 302.
3. The government's proof. Prosecutors put on evidence, often through case agents, tracing each item of proof to an origin that predates or is independent of the immunized testimony.
4. Cross-examination. The Fifth Circuit has held that the substantial burden of Kastigar requires the government to give the defendant a chance to cross-examine relevant witnesses, to test the claim that the evidence is untainted. Cantu, 185 F.3d at 302.

To prepare for such a hearing, careful prosecution teams sometimes use a filter or taint team, wall off exposed lawyers, and preserve pre-testimony reports that document what investigators knew and when. The court may review sensitive material in camera, weigh the credibility of the government's witnesses, and make findings item by item or category by category.

The defense role is to probe every link in the chain: how the government learned of a witness, why the investigation turned toward the defendant, and whether each exhibit or lead traces honestly to a source that owes nothing to the compelled testimony. Gaps in that chain are where a Kastigar motion succeeds or fails.

Remedies and the Standard of Review

When a Kastigar motion succeeds, the consequences scale with the extent of the taint.

The baseline remedy is suppression. Evidence the government cannot trace to an independent source is excluded, along with the further evidence that grew from it. If the tainted proof is central, the case may collapse for want of admissible evidence. Where the exposure reached the grand jury, and tainted evidence helped produce the indictment itself, the remedy can rise to dismissal of the indictment, because the charging instrument is built on constitutionally barred material. In Hubbell, the immunized act of production so pervaded the case that the indictment could not stand. 530 U.S. at 45.

On appeal, review is layered. A trial court's findings about the source of particular evidence are factual and are reviewed for clear error, while the legal questions, such as the proper allocation and scope of the burden, are reviewed without deference. A reviewing court that finds a genuine Kastigar violation may vacate the conviction and remand, and courts have done so when the record shows the defendant was denied the hearing or the independent-source proof the Constitution requires.

Two points temper the picture. Some errors are examined for whether they were harmless, so a defendant wants a clear record that tainted evidence mattered; and remedies are calibrated to the proven taint, so a disciplined motion identifies precisely which items lack an independent source rather than making one sweeping objection.

Where the Kastigar Motion Fits in a Federal Case

A Kastigar motion sits at the intersection of the Fifth Amendment, federal immunity practice, and the law of pretrial motions. It rarely travels alone.

It frequently accompanies or follows related filings. A motion to dismiss the indictment may raise the grand-jury taint that a Kastigar analysis uncovers. A motion to suppress statements may address the voluntariness of the same sessions. Discovery requests may seek the immunity orders, proffer letters, and agent reports that a taint inquiry depends on. And when cooperation is still being negotiated, the terms discussed at the outset determine whether a future Kastigar argument will even be available.

Because the doctrine turns on a precise sequence of events, the earliest moment to protect a client is before any compelled testimony is given. The scope of an immunity order, the wording of a proffer agreement, and a contemporaneous record of what the government already knew can each decide a later motion. Once testimony exists, the focus shifts to reconstructing the timeline and holding the government to its independent-source burden.

The attorneys at L and L Law Group, PLLC, a Frisco, Texas criminal-defense firm, handle federal matters in the Northern and Eastern Districts of Texas. Co-Founding Partners Reggie London (State Bar of Texas No. 24043514; admitted in the Northern and Eastern Districts of Texas and the Fifth Circuit) and Njeri London (State Bar of Texas No. 24043266) address immunity and Kastigar issues as part of federal defense practice. This article is general information about federal procedure and is not legal advice about any specific case.

Common Situations & Variations

This motion comes up in several recurring situations. Each guide below walks through a specific fact pattern, the governing standard, and how Federal courts have handled it.

What the Case Law Says

These decisions—verified against primary sources—control how this motion is litigated. Every case still turns on its own facts.

• Kastigar v. United States, 406 U.S. 441 (1972) — Use-and-derivative-use immunity is coextensive with the Fifth Amendment; a witness who testified under immunity shifts to the prosecution the burden to prove wholly independent sources.
• United States v. Hubbell, 530 U.S. 27 (2000) — The act of producing documents can be testimonial; where compelled under immunity, the government must show its evidence derived independently of that production.
• Murphy v. Waterfront Commission of New York Harbor, 378 U.S. 52 (1964) — The privilege protects a witness across sovereigns; a state immunity grant bars federal use of the testimony and its fruits absent an independent source.
• United States v. Cantu, 185 F.3d 298 (5th Cir. 1999) — At a Kastigar hearing the government must prove an independent source by a preponderance and must let the defendant cross-examine relevant witnesses.

General summaries of published opinions for information only — not predictions about any specific case.