In order to make an arrest, the police need only have "probable cause," or reasonable grounds, to believe a person has committed a crime. The police may temporarily detain a person when there is reasonable suspicion to believe the person has committed or is about to commit a crime. In most cases an arrest is made during the initial investigation. However, in complex "white collar crimes" such as money laundering, or bank fraud or in a case involving a drug trafficking conspiracy, an arrest may not be made until the investigation is complete. In such cases, a prosecutor will often present the matter to a grand jury and obtain an indictment against all the defendants before anyone is arrested.
The indictment is a formal statement of the charges against a defendant. Indictments must be presented to grand juries that consider only the evidence provided by prosecutor. The grand jury then votes to indict or not. In most jurisdictions and in the federal system serious offenses require indictment by the grand jury. However, in some instances a prosecutor may simply file what is called a bill of information. This is not presented to the grand jury. The filing of an indictment or bill of information is merely the formal commencement of the prosecution.
