Introduction

Impeachment and Derivative Evidence

Introduction

A statement taken from a suspect during custodial interrogation is inadmissible unless law enforcement first gave the required warnings and obtained a valid waiver of the rights those warnings describe.¹ Miranda v. Arizona grounded that requirement in the Fifth Amendment privilege against compelled self-incrimination. The Court reasoned that questioning in custody carries inherently compelling pressures that wear down a person's will to resist, so the accused must be effectively told of the privilege and the exercise of it must be honored.² The prosecution carries the burden of showing that those safeguards were in place. The opinion states the consequence in sweeping terms: unless warnings and waiver are demonstrated at trial, "no evidence obtained as a result of interrogation can be used against him."³

Read literally, that sentence leaves the prosecution nothing to do with a defective statement: it cannot be offered for any purpose, and it cannot be used to find anything else. Later doctrine does not read it that way, and a standard statement of the Miranda rule already carries a parenthetical exception for impeachment purposes.⁴ The tension between the broad language and the narrower rule is easiest to see on a concrete set of facts.

Those facts raise two separate questions. The first concerns the defendant's own words: when a defendant chooses to testify, may the prosecution confront the defendant with the earlier unwarned statement, even though it could not have been offered to prove guilt in the first place? The second concerns what the statement produced: when unwarned questioning leads police to a weapon, a witness, or a later confession, does the exclusion of the statement reach that product as well? This chapter takes up the questions in that order, first the use of a defective statement to impeach, then the fate of evidence derived from it, and ends with a working sequence for analyzing any Miranda-defective statement. Every later exception modifies a single baseline, so the lesson begins by fixing exactly what Miranda excludes from the prosecution's proof.