Contact the police
If you are the victim of a crime or a witness to a crime, dial 911 and tell the operator you need the police. Direct the police to where the alleged crime happened. Tell the police what you know. If you are the victim, tell the police you want to press charges.
If the police do not act or if you have discovered the alleged crime after the fact (which is often the case in financial crime), then go to the police department headquarters and tell the desk sergeant that you want to press charges against someone for a crime. The desk sergeant, the person who tends the front desk of a police station, will fill out a form called a "criminal information" report. The criminal information document is a remnant of English common law that underlays much of state and local law in the U.S.
The police will use the details on the criminal information report form to investigate the matter and make an arrest if appropriate. The prosecutor's office will contact you if it needs you to testify or to provide more information to the court. If you are a victim of a crime, tell the prosecutor that you want to pursue the case and want to testify against the defendant.