Proffer agreement
In U.S. criminal law, a proffer agreement, proffer letter, proffer, or "Queen for a Day" letter is a written agreement between a prosecutor and a defendant or prospective witness that allows the defendant or witness to give the prosecutor information about an alleged crime, while limiting the prosecutor's ability to use that information against him or her. As part of the agreement, the subject may agree to create a statement, known as a proffer statement, setting out their testimony.