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Federal Immunity Agreements: Use and Derivative Use Immunity
Federal Immunity Agreements: Use and Derivative Use Immunity
The Protection That Permits Prosecution
The immunity agreement is the federal government’s most effective instrument for compelling testimony it could not otherwise obtain, and its most reliable method for preserving the right to prosecute the very person who provides it. One does not exclude the other. That is the design.
Under 18 U.S.C. § 6002, when the government grants immunity and compels a witness to testify, it forfeits nothing permanent. It relinquishes the ability to use that specific testimony, and whatever evidence flows from it, against the witness. It retains everything else. Every document acquired before the testimony, every cooperating witness developed through independent investigation, every surveillance record and financial filing that existed prior to the compelled statement remains available for prosecution. The protection is real. It is also, if we are being precise, not a shield but a constraint on one avenue of evidence.
Most people who encounter the term “immunity” in a federal investigation believe they are being offered safety. What they are being offered is a transaction. The government receives testimony it could not compel without overriding the Fifth Amendment. The witness receives a prohibition on the use of that testimony. The prohibition has edges, and those edges are where the problems reside.
I have represented clients who signed immunity agreements with confidence and clients who signed them with something closer to resignation. The outcome did not correlate with the emotion.
A Statute Written for the Government’s Benefit
Congress enacted the current immunity framework as part of the Organized Crime Control Act of 1970. The statute replaced the older transactional immunity model, which had barred prosecution entirely for any offense related to the compelled testimony. Transactional immunity was, from the government’s perspective, an unacceptable cost. It required prosecutors to decide, before compelling testimony, whether they were willing to forgo prosecution of the witness for every transaction the testimony might touch. Prosecutors, as a general matter, do not volunteer for constraints of that scope.
The replacement was use and derivative use immunity. Section 6002 provides that no testimony compelled under the order, and no information derived from that testimony, may be employed against the witness in any criminal proceeding, with the exception of a prosecution for perjury or false statements. The statute does not prevent prosecution. It prevents the use of one category of evidence.
The Supreme Court upheld this framework in Kastigar v. United States, 406 U.S. 441 (1972), concluding that use and derivative use immunity was coextensive with the Fifth Amendment privilege. Transactional immunity, the Court determined, afforded more protection than the Constitution required. The decision settled the question. Federal prosecutors have operated under this standard for more than fifty years.
The Burden That Falls on the Government, in Theory
Kastigar imposed a requirement that sounds rigorous in the abstract and proves exceedingly difficult to enforce in practice. If the government prosecutes a witness who has testified under immunity, the prosecution carries the affirmative burden of establishing that all evidence it proposes to use derives from a source wholly independent of the compelled testimony. The burden is not a mere negation of taint. It is an affirmative duty of proof.
In practice, this means the government must demonstrate, for each piece of evidence, that it was obtained through a legitimate independent source. The standard operates like an exclusionary rule applied to an entire evidentiary chain. If a witness under immunity mentions the existence of a second set of financial records, and investigators subsequently locate those records, the government cannot introduce them at trial unless it can establish that it would have discovered them through independent means. The chain of causation matters. Every link in it must be accounted for.
The government does not lose the right to prosecute. It loses the right to benefit, in any respect, from what the witness was compelled to say.
Courts conduct what are known as Kastigar hearings to evaluate whether the government has met this burden. The hearing requires the prosecution to produce evidence of its independent investigative path, often by presenting the testimony of investigators and prosecutors who can attest to the provenance of each piece of evidence. The defense, for its part, need only demonstrate that the witness testified under a grant of immunity to matters related to the prosecution. Once that showing is made, the burden shifts.
Whether this burden is as substantial as Kastigar intended remains, I think, an open question. Justice Marshall, dissenting, observed that the information necessary to evaluate taint resides almost entirely within the government’s possession. A witness who suspects that compelled testimony was used to develop a lead will find it difficult to identify the evidence necessary to prove it. The government controls the investigative record. The defense is left to infer from what the government chooses to disclose.
Seven Kastigar hearings in the Southern District over the past four years produced mixed results, with the government prevailing in most. The pattern is consistent with what practitioners have observed for decades: the hearing exists, the burden is stated, and the government’s institutional capacity to reconstruct an independent evidentiary path is formidable. Whether that reconstruction reflects what actually occurred, or what the government is able to present as having occurred, is a distinction the hearing structure does not reliably capture.
The Proffer Letter and Its Quiet Conditions
Before formal immunity is extended, the government typically conducts what practitioners refer to as a proffer session, sometimes called a “queen for a day.” The nomenclature suggests generosity. The substance does not.
A proffer letter is an agreement under which the witness provides information to the government in exchange for a limited form of protection. In most federal districts, the standard proffer letter provides only use immunity, not derivative use immunity. The distinction is critical and routinely misunderstood. Under use immunity alone, the government agrees that the witness’s own statements will not be introduced against the witness. But the government retains the right to use those statements as investigative leads, to develop new evidence, and to introduce that new evidence in a subsequent prosecution. The derivative path remains open.
The government insists on this structure for a reason. If the proffer collapses and no cooperation agreement follows, the prosecution preserves its ability to pursue the witness without the constraint of proving independent sources for every piece of subsequently acquired evidence. The lesson of United States v. North (which I will address shortly) made federal prosecutors cautious about conceding derivative use protection before the value of the cooperation has been established.
And there is a second condition that receives insufficient attention. The standard proffer letter permits the government to use the witness’s proffered statements for impeachment if the witness later offers testimony at trial that contradicts what was said during the session. The proffer, in this sense, functions as a recorded position. Anything the witness says during the session becomes a constraint on what the witness can say under oath. The practical effect is that the proffer session narrows the witness’s options at trial in ways that are not always apparent at the time the letter is signed.
I have written about the mechanics of proffer sessions in the context of white collar investigations before. The core problem has not changed: the letter looks protective until one examines the conditions under which the protection dissolves.
What Thirty Hours of Televised Testimony Revealed
The prosecution of Lieutenant Colonel Oliver North remains the most instructive case study in the risks of immunized testimony, not because the legal principles were novel, but because the scale of contamination was visible to anyone who owned a television.
In July 1987, North testified before the congressional committees investigating the Iran/Contra affair. Congress had granted him use and derivative use immunity under 18 U.S.C. § 6002. His testimony was broadcast for approximately thirty hours across every major network. The Independent Counsel’s office, which was simultaneously preparing criminal charges, attempted to insulate itself from the testimony. Prosecutors avoided newspapers. They did not watch the broadcasts. They attempted to construct what amounted to an informational quarantine around their own investigation.
North was convicted on three counts in May 1989. The D.C. Circuit vacated the convictions in 1990, concluding that the trial court had conducted an insufficient examination of whether trial witnesses had been influenced by North’s immunized congressional testimony. The court held that even where a witness testifies from personal knowledge, impermissible use within the meaning of Kastigar may occur if the immunized testimony influenced the witness’s decision to testify, shaped the substance of the testimony, or refreshed the witness’s memory.
The government’s failure to sustain the Kastigar burden was, in the D.C. Circuit’s assessment, attributable to the scope of the problem. When immunized testimony is broadcast to the entire country, the prospect of establishing that no trial witness was influenced by it becomes something close to an impossibility. The Independent Counsel could demonstrate that its own team had avoided exposure. It could not demonstrate that every grand jury witness and every trial witness had done the same.
After further hearings, all charges against North were dismissed in September 1991. The case confirmed what defense practitioners had long suspected: derivative use immunity, combined with broad public exposure of the immunized testimony, can render subsequent prosecution untenable. The protection that Kastigar described as coextensive with the Fifth Amendment privilege had, in the North case, functioned as something approaching the transactional immunity the statute was designed to avoid.
Whether the court intended this outcome or merely failed to prevent it is a question worth considering.
Preparation Before the Session Begins
For defense counsel, the period before the proffer session is where the representation either succeeds or produces consequences that cannot be remedied. The government structures the proffer to gather information. The defense must structure its preparation to ensure that the information disclosed serves the client’s interests, or at minimum does not create new avenues of prosecution (which is a narrower goal than most clients realize, and a more honest one).
Competent preparation involves several steps. The attorney must first obtain and review whatever evidence the government has already gathered through independent means, to the extent that evidence has been disclosed. The attorney must then identify the scope of the client’s exposure and determine which facts the client can provide without expanding that exposure. The attorney must negotiate the terms of the proffer letter, paying particular attention to whether the letter provides use immunity only or use and derivative use protection. The attorney must prepare the client for the session itself, which requires both substantive preparation and a candid discussion about the consequences of inconsistency.
- Review all evidence the government has disclosed or is required to disclose
- Map the client’s exposure and identify facts that expand it
- Negotiate the proffer letter terms, with particular attention to derivative use protections
- Prepare the client for the session, including the consequences of inconsistency or later contradictions
- Request that the government memorialize its existing evidence before the proffer, to establish a baseline for any future Kastigar hearing
The fifth step is one that many attorneys neglect. Requesting that the government catalogue and preserve its pre-proffer evidence creates a record against which any subsequent prosecution can be measured. Without that baseline, the Kastigar hearing becomes an exercise in reconstruction rather than comparison, and reconstruction favors the party with greater institutional resources.
The government will not always agree to this request. The refusal itself communicates something about the prosecution’s intentions.
The Anatomy of the Agreement Itself
A formal immunity agreement, whether statutory or informal, contains provisions that determine the scope and durability of the protection. Letter immunity, which is the most common form in federal practice (as opposed to statutory immunity obtained through a court order under § 6003), is a negotiated document. Its terms are not fixed by statute. They are fixed by agreement between the government and the witness’s counsel.
The geographic limitation of letter immunity is a feature that produces consequences with regularity. A letter agreement binds only the office or district that is a party to it. A witness who provides immunized statements to the United States Attorney’s Office for the Southern District of New York is not protected from the use of those statements by the Eastern District, or by a United States Attorney in another state, unless the letter provides otherwise. The standard Department of Justice proffer letter does not, as a default matter, prohibit the disclosing office from sharing immunized statements with other prosecutorial offices. The defense attorney must negotiate this provision into the agreement. Many do not, either through oversight or because the government declines to include it.
The perjury and false statement exception operates as a condition subsequent on the entire agreement. If the government determines that the witness provided false information during the proffer or in subsequent testimony, the agreement dissolves. The witness’s statements become available for use, not merely for impeachment, but as affirmative evidence of a new offense. The false statement statute, 18 U.S.C. § 1001, carries its own penalties, which compound whatever exposure the witness faced before the proffer began. The practical reality is that honesty during the proffer is not merely advisable. It is the structural condition on which the entire protection depends.
There is a tendency among clients to perceive the immunity agreement as a final resolution. It is not. It is a framework that remains operative only so long as its conditions are satisfied, and it protects against only what its language specifies.
The Distance Between the Statute and the Courtroom
The federal immunity framework is, in its statutory form, a precise instrument. The language of § 6002 is clear. The Kastigar standard is well established. The procedural requirements for obtaining a court order under § 6003 are documented in the Justice Manual and have been litigated in every circuit.
Between that precision and what occurs in a conference room on the fourteenth floor of a federal building, there is considerable distance. The proffer session is an adversarial encounter conducted under the appearance of cooperation. The government’s objectives and the witness’s objectives are aligned only to the extent that both parties benefit from the exchange of information, and that alignment can dissolve at any point during the session. I am less certain about this than the preceding paragraph might suggest; the dynamics vary by district, by prosecutor, and by the nature of the investigation. But the structural incentives are not ambiguous.
The distinction between use immunity and derivative use immunity is the single most consequential term in any proffer letter. A client who enters a proffer session under use immunity alone has disclosed information that the government can employ as a roadmap for further investigation. A client who enters under use and derivative use protection has disclosed information that the government must treat as though it was never heard, for evidentiary purposes. The difference is the difference between a statement that constrains the government and a statement that merely constrains the witness.
The invitation to consult with our firm is not incidental to this discussion. A first consultation assumes nothing and costs nothing. It is the point at which the facts of the situation are examined, the scope of exposure is assessed, and the question of whether to cooperate, and under what terms, begins to receive the attention it requires. The federal immunity framework is designed to serve the government’s interests. Competent counsel is the mechanism by which it can also serve yours.