A grand jury is a type of jury, comprised of citizens who are presented with evidence from a state or federal prosecutor (District Attorney or United States Attorney) to determine whether there is probable cause to believe a person committed a crime and should be put on trial. If the grand jury determines there is enough evidence, an indictment will be issued against the defendant. This is known as a “true bill,” and the grand jury is said to have “returned a true bill.” If the grand jury does not believe there is sufficient evidence the accused committed a crime and should be put on trial, it is said to return a “no true bill" or "no bill."

The United States Constitution does not require states to use a grand jury to bring criminal charges against a person—but many states do use grand juries, and some states are required by their state constitution or statutes to use a grand jury to secure an indictment for any felony criminal offense. And the U.S. Supreme Court has interpreted the Constitution to require the federal government to use grand juries for all felony crimes.

Grand jury proceedings are not open to the public and accused persons and their attorneys do not have the right to appear before the grand jury, or to be informed of the proceedings. Witnesses subpoenaed by a grand jury do not have the right to have their attorney present during their testimony. The grand jury proceedings are generally transcribed by a court reporter, but the record is sealed.

Federal grand juries generally consist of 16-23 persons who serve or work on the grand jury for a few days each month for approximately one year—after which a new grand jury is selected by the Federal District Court. At least 12 jurors must agree to return a true bill for indictment of the accused person.

Procedures for the use of grand juries in the state court system vary from state to state and are generally governed by the state’s constitution, and statutes that are often located in the penal or criminal code, the code of criminal procedure, or the government code.

In Connecticut, grand juries are used in accordance with both state statutes and federal law. While the U.S. Constitution does not mandate states to use grand juries, it does require the federal government to use them for all felony crimes, as interpreted by the U.S. Supreme Court. Connecticut law allows for the use of grand juries, but they are not required for all felony charges. When a grand jury is convened, it is composed of citizens who review evidence presented by a prosecutor to determine if there is probable cause to believe a crime has been committed. If they find sufficient evidence, they issue a 'true bill,' leading to an indictment. If not, they return a 'no bill.' Grand jury proceedings in Connecticut are secretive; they are not open to the public, and the accused and their attorneys do not have the right to be present or informed about the proceedings. Witnesses cannot have their attorneys with them during testimony. The proceedings are transcribed and sealed. The size and service duration of federal grand juries are consistent with federal standards, typically consisting of 16-23 members who serve for about a year, with at least 12 jurors needed to indict. State grand jury procedures can vary, and in Connecticut, they are governed by state law, which may be found in the penal or criminal code, the code of criminal procedure, or the government code.