If police question suspects that have been taken into custody without first making them aware of their Miranda rights, they are violating their right to freedom from self-incrimination according to the Fifth Amendment to the United States Constitution. This is due to a momentous 1966 Supreme Court decision in the case of Miranda v. Arizona. The Supreme Court ruled that unless a person in custody is informed of their rights before interrogation, anything that the person says cannot be used as evidence against them at a trail.
The Miranda warning must state that the suspect has the right to remain silent, that anything they say can be used against them in a court of law, that they have the right to an attorney present while they are being questioned, and that if they cannot afford an attorney one will be appointed for them.
The requirement for the Miranda warning applies in any location where suspects have been taken into custody. For instance, whether people have been arrested on city streets, have been put into a police car, or are already at headquarters, they must be informed of their rights before being questioned. However, if suspects have not yet been taken into custody, this stipulation does not apply. For this reason, police officers often postpone arresting suspects until after they have questioned them so that they can obtain incriminating evidence without first informing them of their Miranda rights.
People have no obligation to answer questions put to them by police either before or after arrest with the exception of providing identification. In fact, attorneys generally advise their clients to say nothing until their attorneys are present with them.
Generally, any information that police receive as a result of questioning in-custody suspects without informing them of their Miranda rights is inadmissible as evidence in courts, but there are a few exceptions. For instance, if police obtain weapons, tangible evidence, or further witnesses through questioning without Miranda rights, these things can be used in court against the suspect.