A grand jury, which normally consists of 16 to 23 members, has a specialized function. The United States Attorney, the prosecutor in federal criminal cases, presents evidence to the grand jury for them to determine whether there is "probable cause" to believe that an individual has committed a crime and should be put on trial. If the grand jury decides there is enough evidence, it will issue an indictment against the defendant. Grand jury proceedings are not open for public observation.
Grand juries sit for 18 months and meet 1 to 3 days per month. During a grand juror's term of service, certain days off will be allowed for specific reasons if the juror has been excused in advance. Grand jury service can be somewhat flexible; however, absences should only be requested for truly important reasons since the grand jury must have a quorum of at least sixteen members present to conduct business.
Certificates of attendance are prepared for grand jurors after each monthly session.