By the end of this month, a grand jury is expected to hand down a decision in the case of the shooting of Michael Brown by police officer Darren Wilson in Ferguson, Missouri. One ofthe most frequently considered questions related to the case is, “What exactly is a grand jury?”

Although seemingly shrouded in mystery, grand juries are an essential part of the protections of our liberties within the legal system of the United States. Here is everything you ever needed to know about the grand jury system.

(Note: Most of this information is based on federal grand juries. Grand juries at the state level may have slightly different policies.)

What is a grand jury?

The grand jury is a jury of citizens that determines whether there is probable cause to believe that a crime mitted and that a specific person or mitted it. If the grand jury finds probable cause to exist, then it will return a written statement of the charges called an “indictment.”

After the issuance of an indictment, the case moves to trial where the accused can then defend themselves against the charges brought against them before a petit jury (also called a trial jury).

Why are grand juries important?

Grand juries provide an independent, citizen-based check on the power of the government. A grand jury is able to vote an indictment or refuse to do so, as it deems proper, without regard to the mendations of judge, prosecutor, or any other person.

How do grand juries decide whether to indict?

By an examination of the evidence. Members of a grand jury are even allowed to question witnesses directly. All questions asked of each witness must be relevant and proper, relating only to the case under investigation. Witnesses, of course, may invoke the Fifth Amendment privilege against self-incrimination and refuse to answer a question.

What does a grand jury determine in indictment?

After hearing all the evidence, the members of the grand jury deliberate and take a vote on whether there is sufficient evidence of probable cause to justify bringing the accused to trial. At least 16 jurors must be present and 12 members must vote in favor of the indictment.

Can a grand jury indict anyone they choose?

No. The grand jury must be called by a prosecuting attorney who must also sign the indictment before the case can move to trial. This ensures a government check on a grand jury’s power.

What happens if the grand jury doesn’t indict?

If the evidence does not persuade the grand jury that there is probable cause to believe the mitted a crime, the grand jury will vote a “no bill,” or “not a true bill.” When this occurs, not trial is required for the accused person.

Who presides over the grand jury?

The prosecuting attorney. No judge or defense attorney is present. The accused also has no right to present their case. In some instances, they may not be informed that an accusation is even being made about them to a grand jury.

How many prise a grand jury?

There are 23 members of a federal grand jury. Sixteen of the 23 members of the grand jury constitute a quorum for the transaction of business. If fewer than this number is present, even for a moment, the proceedings of the grand jury must stop.

How long do grand jurors serve?

In the federal system, regular grand juries sit for a basic term of 18 months, but a court can extend this term for another 6 months, bringing the total possible term to 24 months. Special federal grand juries sit for a basic term of 18 months but a court can extend their term for up to another 18 months, bringing their total possible term to 36 months. The term of state grand juries varies widely, but usually last a year.

Do grand juries meet every day?

No, they usually meet once or twice a week.

Is a grand jury required in all cases?

No. An accused person may waive grand jury proceedings and agree to be prosecuted by a written charge of crime called an “information.”

Must grand jury members explain their decision?

Secrecy is an important element in grand jury proceedings. No inquiry may be made to learn what grand jurors said or how they voted, except upon order of the court.

What is “grand jurors’ immunity”?

Immunity is granted to all grand jurors for their authorized actions while serving on a federal grand jury and means that no grand juror may be penalized for actions taken within the scope of his or her service as a grand juror.

Who is chosen for such duty?

Grand juries are chosen much the same way as trial juries: from registered voters or lists of actual voters, or other sources when necessary, under procedures designed to ensure that all groups in munity will have a fair chance to serve.

Federal law requires that a grand jury be selected at random from a fair cross section of munity in the district or division in which the federal grand jury convenes.

How did grand juries get started?

The tradition of using a grand jury goes back to the Magna Carta, the first English constitutional document, which King John granted in 1215 at the demand of his subjects.

The first English grand jury consisted of twelve men selected from the knights or other freemen, who were summoned to inquire into crimes alleged to have mitted in their munity. Grand jurors originally functioned as accusers or witnesses, rather than as judges.

When the English colonists came to America, they brought with them many of the institutions of the English legal system, including the grand jury. This tradition was so important that it was later added to the Bill of Rights. The Fifth Amendment to the U.S. Constitution states that “No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger . . . ”

While all states in the U.S. currently have provisions for grand juries for state-level crimes, only half of the states actually employ them (those states that don’t use grand juries instead use a preliminary hearing before a trial court judge).

Is it true that a prosecutor could, as the old saying goes, “indict a ham sandwich”?

Unclear. There is no record of a federal grand jury ever having indicted an actual ham sandwich.

That famous phrase originated with Sol Wachtler, the former New York State chief judge. In a lunch interview in 1930 with the New York Daily News, Wachtler famously observed that prosecutors have so much control over grand juries that they could convince them to “indict a ham sandwich.”