If an alleged delinquent who is in detention pending trial is not brought to trial within thirty days from the date upon which such detention was begun, the information shall be dismissed on motion of the alleged delinquent or at the direction of the court, unless the Attorney General shows that additional delay was caused by the juvenile or his counsel, or consented to by the juvenile and his counsel, or would be in the interest of justice in the particular case. Delays attributable solely to court calendar congestion may not be considered in the interest of justice. Except in extraordinary circumstances, an information dismissed under this section may not be reinstituted.