In controversial or high-profile cases involving violent crimes or allegations of wrongdoing by a public official, a Maryland prosecutor may choose not to make the charging decision alone, but instead to convene a grand jury to determine whether the individual should be indicted.
A grand jury is a very important component of the criminal justice system, but unlike a criminal trial jury, it does not render a guilty or not guilty verdict. Instead, a grand jury is a group of people who are selected and then asked to decide whether criminal charges should be filed against a potential defendant after viewing evidence presented by the prosecutor. The potential crimes that a grand jury investigates are usually felony charges. Grand juries usually have between 16 and 23 members, while a traditional courtroom jury has between six and 12. They are chosen by the local court system the same way that regular jurists are selected.
Since a grand jury proceeding is not the same as a trial, it is not as formal as a courtroom trial. There is usually only one lawyer present, a prosecutor, and there is no judge or defense attorney. There is no cross-examination and no judgments are handed down. Instead, the prosecution explains the necessary tenets of the law to the grand jury and then evidence and witness testimony are presented. A grand jury is a closed procedure, meaning that everything that goes on during the hearing stays in that room and the members of the grand jury cannot divulge anything about it. This is so any witnesses can speak freely and so that a suspect's reputation is not damaged if the grand jury chooses not to indict.
Unlike a courtroom trial, a grand jury does not need agreement from every member to render a decision, but instead relies on either a consensus by two-thirds or three-quarters of the members. And even if the grand jury decides not to indict a defendant, the prosecution can still charge the suspect if it believes doing so is appropriate.
Source: www.findlaw.com , "How does a grand jury work?", accessed June 1, 2015