The USAG said this on the news conference last night.
The thing is, not being read your rights doesn't mean they don't exist.
The concern is whether or not habeus corpus is denied.
Is this a concern, yup. The a$$hole perp in question IS a naturalized American citizen, so this is squishy, slippery slope ground, regardless of what he did.
The questioning is apparently being done by a "federal government HVT interrogation team"...which makes things even MORE interesting given his citizenship.
The real issue will become IF his brother was the mastermind, and IF this guy has no further contacts or information on other threats, THEN what happens....if he's still held without trial a la enemy combatants...THEN it becomes an even bigger issue, as with no further exigency, there really is no argument, specious or otherwise, for any suspension of rights.
Personally, I think they should have mirandized him right away, ESPECIALLY since the LEOs in the press conference said there was no more threat and the people of Boston can relax....no more immediate threat, no more exigency. Unfortunately, that means the screwed up by immediately after that saying due to public safety exigency, no Miranda. That means if he does get a trial, egg on face of USAG....so get ready for the spin on that one.