A petit jury is a group of people who weigh the facts of a case and return a verdict. Juries are used as a check on the criminal system so that judges are not all-powerful, and they are a common feature of the legal system in many nations. The number of people seated on a petit jury varies by nation, with 12 jurors and two alternates being a common number. As a general rule, all citizens are eligible for jury duty and they may be issued summonses by the government when it is necessary to convene a jury for a trial.
Members of a petit jury are supposed to sit through the trial and listen to the case as it is presented. Once both sides have rested, the judge delivers instructions to the jury which the jury are supposed to use when determining whether or not the defendant is guilty under the law, given the facts presented. A petit jury can return a verdict, and in some cases it may also make recommendations for sentencing and damages.
Petit juries are designed to be drawn from a broad cross section of society, so that the trial is as fair as possible. Before being seated, members of the jury are questioned so that people who would conflict can be struck from the jury. For example, in a rape case, rape victims would not be seated on the jury, because they might have difficulty viewing the case without emotions. People may also be struck because they do not understand the language used in the courtroom, or they lack the mental capacity to evaluate the evidence.
Ideally, a petit jury will be able to return a verdict after deliberating in private over the facts of the case and the instructions from the judge. Sometimes, it is impossible for the jurors to agree, in which case they may indicate that they are “hung” or “deadlocked.” Communications between the jury and the court are usually presented by the foreperson or presiding juror, a member of the jury whom other members elect as a representative.
It is important for members of a petit jury to obey the instructions from the judge, because their role is to determine the veracity of the facts, not the appropriateness of the law. For example, jurors may strongly feel that a defendant is guilty, but the terms of the jury instructions may indicate that they are actually obliged to find the defendant not guilty, given the facts presented. This situation can arise when jurors hear testimony which is later stricken from the record because it is inadmissible. Likewise, jurors may find a defendant committed an offense which they personally feel is not illegal, but they would be required to vote guilty in accordance with instructions from the judge.
A related concept, the grand jury, is a jury which is convened to hear evidence to determine whether there is enough evidence for a trial. If the jury believes that the evidence is firm enough, they can hand down an indictment which will allow the legal system to move to trial. Grand juries usually have more members than petit juries.