Magistrate judge reads Boston Bomber his Miranda rights, whereupon he stops talking. Am I the only one that finds this strange? It was apparently at the initial appearance, held in his hospital room. At the initial appearance, the judge informs the defendant of the charges against him, and reviews conditions of release (obviously, not applicable here), and appoints an attorney if necessary. Rule 5.1, Federal Rules of Criminal Procedure. That's it. No Miranda warnings. I've never heard of anything like this happening.
The Supreme Court has held that a Miranda violation occurs only when resulting testimony is sought to be admitted at trial, not when the questioning occurs. So there was no ongoing violation to be halted, even if a judge had that power. And answers secured without the defendant being Mirandized are still admissible for some purposes, i.e., contradicting his claims at trial (you can't use the statements to prove he is guilty, only to show he's lying when he claims to be innocent. Go figure).
The only sense I can make of it (making the assumption that the judge didn't just want him to shut up) is that the magistrate figured it was a shame that he wasn't being Mirandized, and took it upon herself to do so. I think that calls for impeachment. (Yes, you can impeach a magistrate. You can impeach any Federal employee. The Framers thought the government would be very small, numbering in the dozens or so of decisionmakers, and so made the power broad:
"The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."
"The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behavior...."