An indictment, an information, and a criminal complaint are charging instruments that set forth criminal charges against a defendant and the basis for probable cause to believe the defendant committed a crime.

If a grand jury decides the evidence presented establishes probable cause, it issues an indictment against the accused. In federal criminal prosecutions, at least 12 jurors must vote to indict. The indictment is called a true bill. If the grand jury does not find sufficient probable cause, it returns a no bill.

In a misdemeanor case—or in a felony case where the accused has waived indictment and has agreed to plead guilty—the matter is not presented to the grand jury. In those instances, an information, which is a document outlining probable cause, is filed with the federal district court.

And a criminal complaint is often filed when prosecutors want to make an arrest quickly because a crime is about to occur, or has just occurred. In such a situation prosecutors may not have time to use the grand jury process and will instead file a written criminal complaint, together with an affidavit signed by a government agent familiar with the case. A judge or magistrate judge will then review the complaint and affidavit and issue an arrest warrant if the judge finds probable cause. After an arrest is made based on a criminal complaint, federal law requires the defendant be charged by an indictment—or by a criminal information if it is a misdemeanor case or a felony case where the accused has waived indictment and has agreed to plead guilty—within 30 days.

In state criminal prosecutions, the use of an indictment, information, or complaint as the charging instrument varies from state to state. The requirements and circumstances for such charging instruments are generally located in a state’s statutes—often in the penal or criminal code, or the code of criminal procedure.

In Connecticut, an indictment, information, and criminal complaint serve as formal charging documents in criminal proceedings. An indictment is issued by a grand jury when it finds probable cause to believe a crime has been committed by the defendant. This process involves at least 12 jurors agreeing to indict, resulting in a 'true bill.' If the grand jury does not find probable cause, it returns a 'no bill.' For misdemeanors or felonies where the defendant waives the right to a grand jury and agrees to plead guilty, an information is filed instead. This document outlines the probable cause and is filed with the court. A criminal complaint is used for swift action when a crime is imminent or has just occurred, allowing prosecutors to obtain an arrest warrant based on an affidavit showing probable cause. Under federal law, after an arrest based on a criminal complaint, the defendant must be charged by an indictment or information within 30 days. Connecticut's specific procedures for these charging instruments are outlined in its statutes, which can be found in the state's penal code or code of criminal procedure.