Today, the Court issued an opinion in Fields v. Howe, Case no. 09-1215, in which the Court upheld the granting of a habeas petition based upon a failure to provide Miranda warnings to an inmate in custody at a state facility.
The defendant was a state inmate, incarcerated on charges unrelated to those under investigation. At some point, detectives pulled the defendant from population, placed him a locked room, and interrogated him for up to 7 hours. Although they told the defendant he was free to leave, they did not read him Miranda warnings, and used force (through a corrections officer and by locking the door).
The Court held that "Because Fields was removed from the general prison population for interrogation about an offense unrelated to the one for which he was incarcerated, Mathis is the applicable law. None of the cited appellate cases, all of which were decided subsequent to Mathis, erode its essential holding: Miranda warnings must be administered when law enforcement officers remove an inmate from the general prison population and interrogate him regarding criminal conduct that took place outside the jail or prison."
The Court went so far as to call their ruling a bright line test, requiring - "A Miranda warning must be given when an inmate is isolated from the general prison population and interrogated about conduct occurring outside of the prison."