How a grand jury works

When a grand jury is seated Friday to investigate allegations against McHenry County State's Attorney Louis Bianchi, it will carry on a centuries-old legal tradition in which a group of regular citizens receives broad powers and operates largely under a shroud of secrecy while determining the fate of anyone from a common criminal to the most powerful among us.

Under Illinois law, the grand jury process is one of two ways prosecutors can obtain a determination of probable cause that is needed to bring a person to trial on felony accusations. The other is through a public preliminary hearing presided over by a judge.

Typically, citizens who sit on grand juries are summoned to court for that specific purpose and do not undergo the process known as voir dire, in which attorneys question potential jurors and can remove those they believe would not be receptive to their case.

Grand juries in Illinois usually consist of 16 members, though one can proceed with as few as 12.

Once chosen, grand jurors have authority to subpoena witnesses, documents and other evidence, and ask whatever questions they want as they decide whether there is probable cause to charge someone with a serious crime.

Prosecutors, who serve as advisers to the panel, may also question witnesses, inform grand jurors of the applicable law and possible charges they could bring.

Probable cause, as one attorney who's run dozens of grand jury sessions in McHenry County put it, is "a reasonable belief that a crime may have been committed."

Unlike proceedings before a trial jury, targets of a grand jury probes have no right to testify or call witnesses in their defense, or even be present during the proceedings.

Also unlike trial proceedings, grand jury hearings are held in secret, with no one but the prosecutor, a court reporter, witnesses and those specifically permitted by a judge allowed to attend. Anyone who publicly discusses what was said during a grand jury hearing could be found in contempt of court.

At the end of the proceedings, the jury deliberates and if a majority believes appropriate, hands up indictments, the formal documents accusing someone of a crime and setting them on the path to trial.