Tanner and a co-defendant were tried in federal court and convicted of mail fraud and related offenses. After the jury returned its guilty verdicts, defense counsel received information alleging that several jurors had engaged in serious misconduct during trial—drinking alcohol (including during lunch breaks), using marijuana and cocaine, and sleeping at times during the proceedings and possibly deliberations. Relying on juror affidavits and seeking juror testimony, the defense moved for an evidentiary hearing and a new trial on the ground that the jury was incompetent due to intoxication. The district court granted a hearing but, invoking Federal Rule of Evidence 606(b), excluded juror testimony about jurors' conduct and deliberations. The court instead permitted non-juror evidence, including testimony from courtroom personnel and others who had observed the jurors outside the jury room. After hearing this non-juror evidence, the district court concluded that the defendants failed to establish that juror misconduct deprived them of a fair trial. The Eleventh Circuit affirmed. The Supreme Court granted certiorari to decide whether Rule 606(b) allows juror testimony to show juror intoxication and whether the Sixth Amendment requires such an inquiry.
Does Federal Rule of Evidence 606(b) permit jurors to testify post-verdict that they were intoxicated during trial and deliberations in order to impeach the verdict, and does the Sixth Amendment require an exception to Rule 606(b) for such evidence?
Under Federal Rule of Evidence 606(b), during an inquiry into the validity of a verdict, a juror may not testify about (1) any statement made or incident that occurred during the jury's deliberations; (2) the effect of anything on a juror's mind or emotions as influencing the juror to assent to or dissent from the verdict; or (3) the juror's mental processes concerning the verdict. Juror affidavits on these matters are likewise inadmissible. The rule recognizes narrow exceptions that allow juror testimony about whether (a) extraneous prejudicial information was improperly brought to the jury's attention or (b) an outside influence was improperly brought to bear on any juror. (Modern formulations also allow proof of a clerical mistake in entering the verdict.)
FRE 606(b) bars juror testimony regarding jurors' alcohol and drug use and related inattentiveness because such matters are internal to the jury, not an outside influence. The Sixth Amendment does not require an exception to Rule 606(b) for evidence of juror intoxication. The district court properly excluded juror testimony and, based on the non-juror evidence presented, did not err in declining to order a new trial.
Text and structure of Rule 606(b). The Court read the rule to broadly prohibit juror testimony about their own conduct, mental processes, or the events of deliberations, while allowing testimony only for extraneous information or outside influences. The terms "extraneous" and "outside" refer to influences originating from sources external to the jury, such as media reports, unauthorized documents, bribes, or third-party contact. Jurors' consumption of alcohol or drugs, sleepiness, or inattentiveness are internal conditions of the jurors themselves and thus fall squarely within the prohibition. Common-law background and policy. The decision drew on the longstanding no-impeachment tradition, exemplified by McDonald v. Pless and Mattox v. United States. That tradition protects finality of verdicts, promotes free and frank jury deliberations, and shields jurors from post-verdict fishing expeditions and harassment. Allowing jurors to impeach their own verdict based on claims of intoxication would substantially undermine these interests and invite intrusive post-trial inquiries into jurors' behavior and mental states. Constitutional considerations. The defendants argued that the Sixth Amendment guarantees a trial by a competent and impartial jury and therefore requires an exception to Rule 606(b) for evidence of juror intoxication. The Court rejected this, emphasizing alternative safeguards that adequately protect the right to a fair trial without intruding into jurors' internal processes: (1) voir dire to screen for competence and substance abuse issues; (2) contemporaneous observation by the court, counsel, and courtroom personnel during the trial; (3) the availability of juror complaints to the court during trial; and (4) the admissibility of non-juror evidence of misconduct at a post-trial hearing. Indeed, the district court in this case allowed non-juror testimony, but the showing was insufficient to disturb the verdict. Given these safeguards, a constitutional exception was unwarranted. Application. Because the alleged misconduct involved jurors' internal behavior and condition, juror testimony was inadmissible. The district court's decision to confine the inquiry to non-juror evidence complied with Rule 606(b), and its refusal to order a new trial was not an abuse of discretion.
Tanner establishes the modern internal/external distinction under Rule 606(b) and powerfully reinforces the no-impeachment rule. It teaches that post-verdict challenges based on juror intoxication, inattentiveness, or similar internal misconduct cannot rely on juror affidavits or testimony. Instead, parties must marshal non-juror evidence and, ideally, raise the issue during trial when the court can intervene. Tanner has been repeatedly cited to bar juror testimony about internal matters (e.g., Warger v. Shauers) and remains the default rule in federal courts. Its constitutional holding has one notable limit: Peña‑Rodriguez v. Colorado later recognized a narrow Sixth Amendment exception requiring inquiry into clear statements of racial animus during deliberations. Outside that narrow context, Tanner controls.
Tanner v. United States entrenches the federal no-impeachment rule's bright line: juror testimony cannot be used to prove internal misconduct such as intoxication, inattentiveness, or mental processes affecting a verdict. Instead, litigants must rely on non-juror evidence and raise concerns in real time so the trial court can implement remedies that protect the defendant's Sixth Amendment rights without compromising the integrity and finality of jury deliberations.