A petit jury — also called a trial jury — is a type of jury that hears all the facts of a case during a criminal trial and renders a verdict. The size of a jury varies by both jurisdiction and type of case, though a common number of jurors is 12. Petit juries are different than other kinds of juries, such as grand juries, which determine whether or not there is enough evidence to charge the defendant with the alleged crime. The process for being selected to a petit jury also varies from jurisdiction to jurisdiction, but it is often a requirement of citizenship to make oneself available to serve when needed.
The purpose of a petit jury is to consider all the evidence presented at trial and determine whether or not the accused is guilty. After all the evidence is presented, the judge will remind the petit jury of their task, along with any instructions that the judge deems appropriate for them to consider in their deliberations. The proportion of the total jury that is required to agree in order to render a guilty verdict varies from jurisdiction to jurisdiction. Some jurisdictions require a majority of jurors, while others require a unanimous decision.
A petit jury differs from a grand jury in both its purpose and size. Grand juries, which are no longer used in most jurisdictions, are typically used in a special proceeding where the prosecutor presents all possible evidence that may be used against the accused in a potential trial. This kind of jury considers the evidence and if it determines that there is enough evidence to justify a trial, then the accused may be formally charged with the crime. Additionally, grand juries are usually comprised of around 20 members, while a petit jury is usually comprised of 12 members.
The process by which people are compelled to serve on a petit jury varies by jurisdiction. Most jurisdictions require that citizens report to potentially serve on a jury when needed, usually once every three years. Typically, there will be a large pool of members from which the attorneys may select the jurors in a process called voir dire. During this process, the attorneys and the judge will ask each potential juror about his or her history in order to determine the possibility of any bias inherent in the juror that would impair his or her ability to impartially consider the facts. After whittling the pool down to the appropriate number, the case will commence.