Kent and I have posted on the law governing terrorist interrogation. The rules are unsatisfactory, largely because neither Miranda nor the limited exception to Miranda explained in Quarles was designed for the world of terrorist warfare.
Another sensible explanation is set forth in this article in Atlantic magazine. Its penultimate paragraph is a good sample:
[I]n a case such as this one, where it seems likely both that the government will have overwhelming evidence to convict (without relying on any post-arrest statements) and that Tsarnaev may be in possession of valuable information that implicates national security, the rationale behind the government's choice emerges: Even if the public-safety exception is determined to have been wrongfully invoked, this would not threaten the government's case in a meaningful way. One may certainly contest whether the Court's shifting on Miranda is correct or whether the government's choice not to Mirandize Tsarnaev is desirable as a policy matter. Nor have the media been wrong to question the government's broad interpretation of the public-safety exception. But it is misleading to paint the decision not to Mirandize as trampling Tsarnaev's constitutional rights as an American citizen.
In fact, and as I expect to explain in a later post, Eric Holder is on shaky ground in thinking that the Quarles exception will carry him as far as he seems to think it will. It might or it might not. What is actually needed is for the Court to revisit Miranda itself, which was incorrect the day it was decided and is increasingly a relic of a different time in any event. But that is beyond the scope of my present ambition.