Police officers may open closed containers while conducting a routine inventory search of an impounded vehicle. See Colorado v. Bertine 479 U.S. 367 (1987). The underlying rationale for allowing an inventory exception to the Fourth Amendment warrant rule is that police officers are not vested with discretion to determine the scope of the inventory search. See South Dakota v. Opperman, 428 U. S. 364, 428 U. S. 382-383 (1976) (POWELL, J., concurring). This absence of discretion ensures that inventory searches will not be used as a purposeful and general means of discovering evidence of crime. Thus, it is permissible for police officers to open closed containers in an inventory search only if they are following standard police procedures that mandate the opening of such containers in every impounded vehicle.