Just about every cop show fan knows about Miranda rights. The cop reads something like this to the prisoner off a card taped to the inside of his cap:
You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to an attorney. If you cannot afford an attorney, one will be appointed to you.
There is a lot of misunderstanding about the Miranda warning, however. The most common error is that the warning is always required when a suspect is taken into custody. Not so. It is not required as a matter of constitutional law.
Police, therefore, may not "Mirandize" a suspect in every case. The consequence of not doing it is that any incriminating statement made by a suspect may not be used against him at trial.
Failure to state the warning is not a violation of due process either, as some may think.
Miranda is what is known as an exclusionary rule. In other words, a confession is excluded as evidence in a trial if the suspect was not advised of his right to remain silent. It doesn't matter if the prosecutor has enough independent evidence to convict anyway. A suspect does not go free because the cops didn't read him his rights.
Also, interrogators can use anything the detainee says for other purposes (for example, in gathering intelligence). This is the crux of the controversy over if and when Miranda rights should be read to suspected terrorists.
The Miranda warning is derived from a 1966 Supreme Court decision called Miranda v. Arizona. The Court stated that a "person in custody must, prior to interrogation, be clearly informed that he or she has the right to remain silent, and that anything the person says will be used against that person in court; the person must be clearly informed that he or she has the right to consult with an attorney and to have that attorney present during questioning, and that, if he or she is indigent, an attorney will be provided at no cost to represent her or him."
Ernesto Miranda was convicted of rape. Part of the evidence was a coerced confession. After the Supreme Court decision, Miranda was retried and convicted. This time his confession was not introduced into evidence at the trial. Four years after his parole, he was stabbed and killed in a bar fight.