According to the Fourth Amendment of the U.S. Constitution, the police can only arrest a person when they have probable cause, which means that they have to have a good reason to believe there's been a crime and that the suspect committed it. A judge will later decide whether or not there was probable cause to detain the suspect, and if there was not, the detainee will be released. At the time of arrest, the police must inform the suspect of his or her constitutional rights, including the rights to remain silent and to consult an attorney. If the suspect is charged with the crime, a prosecutor decides whether to bring criminal charges, and which crime or crimes the suspect is to be charged with. In felony cases, or crimes for which the penalty could be one year or more in jail, prosecutors may enlist the help of a grand jury. In most states, prosecutors must file charges against a suspect held in custody within 72 hours of arrest, but some states require this even sooner. In California, for example, a charge must be filed within 48 hours of arrest. The prosecutor can alter the nature of the charge at a later date. Once charges have been filed, the suspect will be arraigned in court, at which time the suspect may be formally charged with the crime and be given the opportunity to plead guilty or not guilty.
