Here's the joker.
In Edwards v. Arizona, the U.S. Supreme Court ruled that once a custodial suspect has invoked the Miranda right to counsel, he is not subject to further police-initiated questioning on that case unless and until counsel is provided. The court carried this rule one step further in Arizona v. Roberson, ruling that a suspect who has requested counsel may not be questioned as to any case unless counsel is present.
Years later, in Minnick v. Mississippi, the court held that even if a requested attorney had been provided on the first case, the suspect could not be questioned on any other case unless the attorney was present. In dissent, Justice Scalia pointed out that under this ruling, a suspect who invoked counsel and then remained in continuous custody could not be approached "three months, three years, or even three decades later" to seek a waiver and a statement on any case, unless counsel were present.
Scalia's worry was about to be tested in a 1993 case called U.S. v. Green. Lowell Green was arrested for drugs and invoked his Miranda right to counsel. He was tried, convicted, and sentenced to incarceration without having been released (a release erases an invocation and starts Miranda all over again upon rearrest, per McNeil v. Wisconsin). Three months later, different officers investigating an unrelated murder visited Green in jail and obtained a Miranda waiver and a confession.
At his murder trial, Green was allowed to suppress his confession, on grounds that the officers' questioning violated the Edwards-Roberson-Minnick rule prohibiting any subsequent questioning after a suspect in continuous custody has invoked his right to counsel under Miranda. An appeal was taken to the U.S. Supreme Court, but while the case was pending, Green died in custody. The court dismissed the case as moot, and it has never taken another case to test whether the Minnick ruling indefinitely prevents police-initiated interrogation of a suspect who has remained in continuous custody since invoking his Miranda right to counsel.