The rules governing grand jury proceedings are very different from those governing trials by (petit) jury. The public is not admitted to hearings, and witnesses can be compelled to testify. The procedure is inquisitorial rather than adversarial: the defense is not allowed to call witnesses, and the prosecutor is not obliged to present both sides of the case. Hearsay and other evidence that might be excluded at a jury trial may be introduced.
The use of grand juries has declined in the 20th cent., in part because they were perceived as prone to either prosecutorial domination or abuse of their investigatory role. Britain abandoned them in the 1930s, and today fewer than half of U.S. states employ them. The information, a written statement issued by a prosecutor, has largely replaced the indictment. The Fifth Amendment to the U.S. Constitution, however, guarantees a grand jury inquiry to anyone accused in federal court of a capital "or otherwise infamous" (i.e., a felony) crime.
In the early decades of the United States grand juries played a major role in public matters. During that period counties followed the traditional practice of requiring all decisions be made by at least 12 of the grand jurors, so that for a size of 23 a bare majority would be 12. Any citizen could bring a matter before it directly, from a public work that needed repair, to a delinquent official, to a complaint of a crime, and they could conduct their own investigations. In that era most criminal prosecutions were conducted by private parties, either a law enforcement officer, a lawyer hired by a crime victim or his family, or even by laymen, who could bring a bill of indictment to the grand jury, and if the grand jury found there was sufficient evidence for a trial, that the act was a crime under law, and that the court had jurisdiction, then by returning the indictment to the complainant, it appointed him to exercise the authority of an attorney general, that is, one having a general power of attorney to represent the state in the case. The grand jury served to screen out incompetent or malicious prosecutions. The advent of official public prosecutors in the later decades of the 19th century largely displaced private prosecutions, but also led to them capturing grand juries and using them in ways for which they were not originally intended.
In Ireland grand juries were active from medieval times in the English-controlled parts of the island, mainly functioning as local government authorities at the county level, as well as having a pre-trial judicial function for serious criminal cases. Members were usually wealthy landowners, farmers and merchants, who selected new members. From 1691 to 1793 Roman Catholics were excluded from membership. They were replaced by democratically-elected County Councils by the Act of 1898.
A grand jury is meant to be part of the system of checks and balances, preventing a case from going to trial on a prosecutor's bare word. A prosecutor must convince the grand jury, as an impartial panel of ordinary citizens that there exists reasonable suspicion, probable cause, or a prima facie case that a crime has been committed. The grand jury can compel witnesses to testify before them. Unlike the trial itself, the grand jury's proceedings are secret; the defendant and his or her counsel are generally not present for other witnesses' testimony. The grand jury's decision is either a "true bill" (meaning that there is a case to answer) or "no true bill". Jurors typically are drawn from the same pool of citizens as a petit jury, and participate for a specific time period.
The composition of the grand jury was taken from that of a minor sanhedrin, which under Jewish law, empaneled 23 judges with a quorum requirement of 13.
Cato Institute writers argued that grand juries as conducted today are unjust as the defendant is not represented by counsel and/or does not have the right to call witnesses. Intended to serve as a check on prosecutors, the opportunity it presents them to compel testimony can in fact prove useful in building up the case they will present at the final trial.
In practice, a grand jury rarely acts in a manner contrary to the wishes of the prosecutor. Judge Sol Wachtler, the former Chief Judge of New York State, was quoted as saying that a prosecutor could persuade a grand jury to "indict a ham sandwich. On the other side, many prosecutors argue that the screening function of the grand jury operates with greater effect on a prosecutor's decision to bring a case in the first place; though records are understandably difficult to come by, many prosecutors say they simply do not bring cases to the grand jury that they believe the grand jury will not indict. In this way, grand juries may exert more of a check on prosecutors than the "ham sandwich" remark suggests.
Many jurisdictions in the United States have replaced the formality of a grand jury with a procedure in which the prosecutor can issue charges by filing an information (also known as an accusation) which is followed by a preliminary hearing before a judge at which both the defendant and his or her counsel are present. New York has amended procedures governing the formation of grand juries so that grand jurors are no longer required to have previous jury experience.
Contrary to what some might expect, in some jurisdictions grand jurors are selected to serve by the local prosecutor, rather than by random selection from the community. Many who serve have done so many times and have a proven "record" to indict. No state has a provision to limit the number of grand juries a prosecutor can form to finally get the indictment he wants. If the first one doesn't indict he can form another. This issue was identified nationally when Texas prosecutor, Ronnie Earle, organized three grand juries before he could get an indictment on Congressman Tom Delay. The issue is mitigated by the fact that each subsequent grand jury may be called to view additional evidence, and not to merely revisit evidence that was already presented (tellingly Earle was eventually vindicated by uncovering the Jack Abramoff Indian lobbying scandal).
The Constitutionality of contemporary grand jury practices has been brought before the Supreme Court six times in history; however, the court has yet to allow a case to be heard. According to Mike Martin, former Texas State Representative in an interview with the Austin American Statesman in 1982, "A grand jury is nothing more than a perjury trap. They drag you in by court order, won't let you have an attorney present, tell you the Fifth [Amendment] doesn't apply because you are not accused of anything, then slap a felony charge on you at the end because you deny an accusation. It goes against everything our forefathers intended when they set up America's judicial system".
In some rare instances, the grand jury does break with the prosecutor. It can even exclude the prosecutor from its meetings and subpoena witnesses and issue indictments on its own. This is called a "runaway grand jury." Runaway grand juries sometimes happen in government corruption or organized crime cases, if the grand jury comes to believe that the prosecutor himself has been improperly influenced. Such cases were common in the 19th century, but have become infrequent since the 1930s.
In all U.S. jurisdictions retaining the grand jury, a potential defendant has the right under the Fifth Amendment not to give self-incriminating testimony. However, the prosecutor can call a potential defendant to testify and which may require that person to then assert their Fifth Amendment right.
In California, each county is required by the state constitution to have at least one grand jury impaneled at all times. Grand Juries are governed by Title 4 of the California Penal Code, as well as other more general provisions. Grand juries are not subject to the Brown Act.
Most grand juries are seated on a fiscal cycle, i.e. July through June. Most counties have panels consisting of 19 jurors, some have as few as 11 jurors, others have as many as 23 (see California Penal Code Section 888.2). All actions by a grand jury require a two-thirds vote. Jurors are usually selected on a volunteer basis.
These county-level grand juries primarily focus on oversight of government institutions at the county level and lower. Almost any entity which receives public money can be examined by the grand jury, including county government, cities, and special districts. Each panel selects the topics which it wishes to examine each year. A jury is not allowed to continue an oversight from a previous panel. If a jury wishes to look at a subject which a prior jury was examining, it must start its own investigation and independently verify all information. It may use information obtained from the prior jury but this information must be verified before it can be used by the current jury. Upon completing its investigation, the jury may, but is not required to, issue a report detailing its findings and recommendations.
The grand jury is required to publish a minimum of one report containing a minimum of one finding and one recommendation. The published reports are the only public record of the grand jury's work; there is no minority report. Each published report includes a list of those public entities which are required or requested to respond. The format of these responses is dictated by California Penal Code Section 933.05, as is the time span in which they must respond.
County grand juries develop areas to examine by two avenues: juror interests, and public complaints. Complaints filed by the public are kept confidential. The protection of whistleblowers is one of the primary reasons for the confidential nature of the grand jury's work.
Most county grand juries in California do not consider criminal matters, though by law they are able to. The decision of whether or not to present criminal cases to the grand jury is made by the county District Attorney.
The law governing county grand juries may differ in Nevada.
Hennepin County, Minnesota (which contains Minneapolis) keeps a Grand Jury impaneled at all times. Each Grand Jury serves a term of four months. The Grand Jury typically meets one day each week. It focuses almost exclusively on homicide cases.
In Kentucky, grand jurors are empaneled in each county, at the Circuit level (felonies only) for a four-month term (3 panels per year). During the trial jury orientation for the given four-month term, the grand jurors are selected from the trial jury pool, although the method of selection is not necessarily random. The meetings are twice a month (however, grand juries in more populous counties generally meet more often), with each meeting usually going through 20-30 cases in a 4-5 hour period. The indictment rate is about 98-99%; the grand jury can broaden (about 1% of the time) or narrow (about 3% of the time) the counts in the indictment as well. Usually, 15 or so grand jurors are required to report to meetings; the hope is that 12 will show to each meeting, which is the number of jurors required to hear cases (extra jurors can leave). It takes 9 yes votes to the question of probable cause to sign a true bill of indictment. Less than 9 yes votes either causes a no true bill or a narrowing of the indictment (depending on the votes per count).
The rules are very similar to the federal process; the grand jury only hears from law enforcement personnel, with the exception of property crimes, where store detectives or actual victims of theft or vandalism are called to testify. The only cases brought to the grand jury are those initiated from the Commonwealth's Attorney's office (the prosecutor for felonies). For the vast majority of cases, the grand jurors generally only hear a recitation of facts from the police report, crime laboratory reports, and other documentation generated during the evidence gathering process. Grand jurors can ask factual questions of the witnesses and legal questions of the prosecutors. The ability to broaden or narrow indictments does technically allow for grand juries to open new avenues of investigation, although since it is dependent on prosecutors for facts, this seems very rarely done, if ever. Rules of confidentiality apply to grand jurors, which are similar to the federal rules.