Didn't Dzhokhar Tsarnaev have the same right as Abdulmutallab, and weren't officials legally required to inform him of it? Well, not quite. The right in question is not, strictly speaking, a right to remain silent. Rather, it is derived from the Fifth Amendment, which guarantees that a defendant in a criminal case may not be compelled to be a witness against himself. But if an interrogation is being conducted to gather information, not to build a criminal case, then no right to remain silent exists. Law enforcement already has a surfeit of evidence--including photographs and videos of him at the scene of the bombing. The HIG interrogators weren't trying to help prosecutors construct their case.
Of course, Mr. Tsarnaev could have chosen not to talk to intelligence interrogators, or chosen to lie to them. But that is what he would have been exercising: a choice, not a right.
Wasn't there a requirement that Mr. Tsarnaev be brought without delay before a judge? Again, not quite. The rule in question requires that defendants be taken to court without unnecessary delay--but the rule has been interpreted in one case from the judicial circuit that includes Massachusetts to permit even a hiatus of almost four months between arrest and court appearance when a defendant was in state custody during that period. The circuit court found that so long as the delay wasn't used to obtain a confession, it was not unreasonable.
And what of the right to counsel? Didn't Mr. Tsarnaev have the right to a lawyer, and to have that lawyer present during any questioning? Once more, not quite. Another amendment, the Sixth, guarantees the right to counsel in a criminal case, but it guarantees no more.
If Mr. Tsarnaev was being questioned by the HIG solely to gather intelligence, and no admission of his or lead from information he disclosed was to be used in his criminal case, then he was no more entitled to a lawyer in connection with such questioning unrelated to his criminal case than he was entitled to a lawyer to close a real-estate transaction. The HIG could have easily ensured that none of the fruits of its questioning could be used in the criminal case.
Ideally, such intelligence questioning would have continued for a long period, probably months, so that interrogators could try to substantiate the information they obtained, then double back and ask more questions based on what they found. Intelligence-gathering is an incremental process, at best.