The rationale of Miranda holds that (1) a person confronted with custodial police interrogation is presumed to be so stressed by the experience that he or she will feel compelled to answer questions and make statements; (2) the Fifth Amendment forbids compelled self-incrimination; and therefore (3) statements obtained from custodial interrogation are inadmissible to prove guilt at trial; unless (4) the presumed compulsion has been neutralized by the now-familiar four-part warning.
The Miranda opinion gave lower court judges, lawyers, and police officers what Chief Justice Warren described as "concrete constitutional guidelines" for applying the Miranda rules: the warnings would be required in order to make a statement admissible if police interrogation occurred after the suspect had been "taken into custody or otherwise deprived of his freedom in any significant way." This "concrete" definition of "custody" proved to be more like quicksand.
Of the 55 subsequent Supreme Court opinions on Miranda issues, 14 have involved attempts to clarify the meaning of "custody," and in 12 of those 14, the Supreme Court reversed the decisions of state and federal appellate courts, which got it wrong. No wonder the Supreme Court has now admitted that "the task of defining 'custody' is a slippery one." (Oregon v. Elstad)
Three Supreme Court rulings have dealt with the particular problem of deciding whether Miranda applies when officers go to a jail or prison to question an inmate. If the suspect is already incarcerated, isn't he under even greater restraint than when, like Ernesto Miranda, he’s simply handcuffed and taken to the station under arrest? The first encounter with this issue arose in 1968, only two years after Miranda v. Arizona was decided.
Mathis v. U.S.
Robert T. Mathis was an inmate in a Florida prison on state convictions when federal agents went there to question him about tax crimes. They gave no Miranda warnings. Mathis made incriminating statements which were used to obtain his conviction. On appeal to the U.S. Supreme Court, Mathis claimed that he should have been Mirandized, and the court majority agreed. Repeating the "concrete" definition of "custody" contained in the Miranda decision, the court ruled that Mathis was subjected to custodial interrogation without warnings, and his convictions were reversed.
In dissent, three justices (who had also dissented in Miranda) disagreed with the court's finding of "custody." These justices pointed out that as an inmate accustomed to the prison environment, Mathis was in familiar surroundings when he was questioned, which should have dispelled the presumption of compulsion that arises when a person at-large is arrested by the police and taken in for questioning.
The rationale advanced by the Mathis dissenters was subsequently adopted by some lower courts to distinguish inmate interrogation from arrestee interrogation. (U.S. v. Willoughby—2nd Circuit; U.S. v. Cooper—4th Circuit; U.S. v. Menzer—7th Circuit; U.S. v. Ingle—8th Circuit; U.S. v. Turner—9th Circuit; U.S. v. Grimes—11th Circuit) It was not until 2010 that the Supreme Court next considered the issue of inmate "custody."