## Facts

- A federal grand jury indicted Mechanik and Lill on drug offenses, including conspiracy; a superseding indictment broadened the conspiracy allegations.
- In seeking the superseding indictment, two law-enforcement agents testified together before the grand jury.
- The defendants learned of the joint testimony during the second week of trial after receiving grand-jury transcripts.
- A petit jury convicted the defendants on the conspiracy counts.
- After the guilty verdict, defendants moved to dismiss the superseding indictment, claiming the joint testimony violated Federal Rule of Criminal Procedure 6(d), which restricts attendance to specified persons, including “the witness under examination.”
- The district court denied the motion.
- The Fourth Circuit reversed the conspiracy convictions and dismissed the conspiracy portion of the indictment based on the Rule 6(d) violation.
- The Supreme Court granted review.

## Issues

1. Whether a petit jury’s guilty verdict renders harmless a Rule 6(d) violation affecting the grand jury’s charging decision, making post-verdict dismissal of the indictment improper.
2. Whether a post-conviction challenge to an indictment may succeed where the asserted grand-jury error did not affect the fairness of the trial.

## Decision

- The Supreme Court held that the petit jury’s guilty verdict rendered harmless any Rule 6(d) error that might have influenced the grand jury’s charging decision.
- The Court concluded that dismissal of the indictment after conviction was unwarranted where the alleged defect concerned the grand jury’s probable-cause determination rather than the validity of the trial.
- The Court emphasized that the costs of retrial after a valid guilty verdict are too high to justify setting aside convictions based solely on non-constitutional grand-jury irregularities.

## Legal Principles

- A guilty verdict beyond a reasonable doubt establishes not only probable cause but actual guilt, generally curing prior errors that relate only to the grand jury’s charging function.
- Under Federal Rule of Criminal Procedure 52(a), courts must disregard errors that do not affect substantial rights; post-verdict, many Rule 6(d) violations fall into this category when the trial was fair.
- Post-conviction relief for grand-jury irregularities is generally inappropriate absent an effect on trial fairness or reliability of the verdict.
- Non-constitutional procedural violations in grand-jury proceedings differ from structural constitutional defects (e.g., discriminatory grand-jury selection), which may require reversal to protect the justice system and deter misconduct.

## Conclusion

The Court ruled that, once defendants are convicted by a petit jury, most non-constitutional grand-jury procedural errors—such as a Rule 6(d) violation involving witness presence—are harmless as to the charging decision and do not justify dismissing the indictment after verdict.


United States v. Mechanik, 475 U.S. 66 (1986)