The right to trial by jury in criminal cases is guaranteed by the Sixth Amendment to the U.S. Constitution, as well as the laws of every state. (See The Right to Trial by Jury.) Lawyers and judges select juries by a process known as "voir dire," which is Latin for "to speak the truth." In voir dire, the judge and attorneys for both sides ask potential jurors questions to determine if they are competent and suitable to serve in the case. Errors during jury selection are common grounds for appeal in criminal cases.
When a case is called for trial, a randomly selected panel of potential jurors (called a venire) is seated in the courtroom.
The trial judge begins voir dire by asking the prospective jurors questions to ensure that are they are legally qualified to serve on a jury and that jury service would not them cause undue hardship. For example, most states allow a student who might miss critical exams, a person who has an upcoming surgery scheduled, or someone who serves as sole caretaker of an ill or elderly family member to be excused from jury service for undue hardship.
Next, the lawyers for each side question the potential jurors about their biases and backgrounds, as well as any pre-existing knowledge they might have about the case. The attorneys can also ask questions designed to uncover characteristics or experiences that might cause potential jurors to favor either the prosecution or the defense. But the lawyers aren't allowed to ask overly personal questions, and they aren't allowed ask the jurors how they would decide the case in advance.
After they have completed questioning, the lawyers begin removing potential jurors from the venire by making challenges for cause and peremptory challenges.
Challenges for cause are made when voir dire reveals that a juror is not qualified, able, or fit to serve in a particular case. Lawyers generally have an unlimited number of "for cause" challenges available.
In order to serve as a juror, a person must be a U.S. citizen, over the age of 18, live in the court's jurisdiction, and have the right to vote. Also, each person must be able to physically sit through the entire trial as well as hear and understand the trial testimony. Jurors must also be mentally aware enough to comprehend and apply the judge's legal instructions. Any person who doesn't meet these criteria will be dismissed "for cause."
Judges will also dismiss jurors who can't put aside their feelings and apply the law impartially—that is, without actual or implied bias.
Actual Bias. Actual bias arises when potential jurors admit that they wouldn't be able to be impartial. For example, a juror who states that she would never vote for a guilty verdict in any case because her religious beliefs prevent her from sitting in judgment of another would be excused for cause.
Implied Bias. Implied bias is present when potential jurors have character traits or personal experiences that make it unlikely for them to be able to be impartial, regardless of what they say during voir dire. So, a juror who is a close friend or relative of a key party, a witness, the judge, or an attorney for either side will be dismissed for cause. Bias is also implied when a would-be juror's background or experience is likely to create a predisposition in favor of a party to the case. For example, in a case involving school teachers accused of fraudulently misrepresenting standardized test scores, any teachers in the panel will probably be excused for cause (even if those teachers swear in voir dire that they can be impartial).
No reason is required for a lawyer to use a peremptory challenge to excuse a potential juror. Such challenges allow each side to dismiss jurors who are otherwise qualified, but appear likely to favor the opposing party. However, peremptory challenges cannot be used to exclude jurors on the basis of race or class. Lawyers only have a specified number of peremptory challenges available—that number varies from state to state and depending on the nature of the case (a misdemeanor, felony, or death penalty trial).
In the process known as "striking a jury," the prosecution and defense take turns arguing their challenges for cause. If the judge grants a challenge, the juror will be struck from the jury panel. Once there are no more viable challenges for cause, the sides alternate in striking jurors via peremptory challenges until those are exhausted or each side is satisfied with the jury panel. Some states require all challenges to be made orally, while others allow for written peremptory challenges.
The states vary in the number of jurors required for a jury, ranging from
six to 23. If too many potential jurors have been eliminated after the use of challenges, the judge can either summon additional potential jurors or declare a mistrial.
Once the challenges are completed and there are enough jurors for a proper jury, the judge will place the remaining jurors in the jury box.
If the attorneys have any challenges to the demographic composition of the jury (claims that the other side used peremptory strikes to eliminate jurors on the basis of race, ethnicity, or gender), they must assert them at this time. Then, the jurors are sworn in, which ends jury selection and begins the next stage of the trial process.