A jury is group of people empowered to make findings of fact. During a court trial, the jury decides the truth of disputed facts while the judge decides the rules of law, including whether particular evidence will be presented to the jury.
The United States Constitution guarantees the right to trial by jury for most criminal and many civil matters. See Amendments V, VI, and VII. The right to a jury does not extend to prosecution for petty criminal offenses. See, e.g., Duncan v. State of La., 391 U.S. 145, 159 (1968). Generally, a petty offense is a crime that is punishable by a sentence of six months or less.
In federal court, a jury consists of 12 members although smaller juries are constitutionally acceptable. See, e.g., Williams v. Florida, 399 U.S. 78 (1970) (upholding a six-person jury). Generally, a jury verdict in federal court must be unanimous. Parties to a case may agree to waive any jury rights at any time before a verdict is returned. See Federal Rules of Criminal Procedure 23.
Absent fraud, a jury verdict is final. Jury deliberations will not be scrutinized, or their verdict overturned, even when the jury is suspected to have purposefully rejected the judge’s instructions or the evidence presented. See Jury Nullification.
See CRS Annotated Constitution: