The scenario has been used to justify torture in the past. But here, it is being used to justify employing the public safety exception to Miranda. Emily Bazelon, writing in Slate, makes some excellent points about the exception, and explains how it has been used previously:

There is one specific circumstance in which it makes sense to hold off on Miranda. It’s exactly what the name of the exception suggests. The police can interrogate a suspect without offering him the benefit of Miranda if he could have information that’s of urgent concern for public safety. That may or may not be the case with Tsarnaev. The problem is that Attorney General Eric Holder has stretched the law beyond that scenario. And that should trouble anyone who worries about the police railroading suspects, which can end in false confessions. No matter how unsympathetic accused terrorists are, the precedents the government sets for them matter outside the easy context of questioning them. When the law gets bent out of shape for Dzhokhar Tsarnaev, it’s easier to bend out of shape of the rest of us.

[...]

Things start to get murkier in 2002, after the FBI bobbled the interrogation of Zacarias Moussaoui, the 20th 9/11 hijacker—the one who didn’t get on the plane—former FBI special agent Coleen Rowley wrote a memo pleading that “if prevention rather than prosecution is to be our new main goal, (an objective I totally agree with), we need more guidance on when we can apply the Quarles ‘public safety’ exception to Miranda’s 5th Amendment requirements.” For a while, nothing much happened.

Then the Christmas Day bomber, Umar Farouk Abdulmutallab, was apprehended in December 2009, before he could blow up a plane bound for Detroit. The FBI invoked the public safety exception and interrogated. When the agents stopped questioning Abdulmutallab after 50 minutes and Mirandized him—after getting what they said was valuable information— Abdulmutallab asked for a lawyer and stopped talking. Republicans in Congress denounced the Obama administration for going soft.

Bazelon worries that the public safety exception will be abused by authorities if it is used unjudiciously. This is certainly something that should concern all of us.

But when authorities are confronted with so many unknowns regarding Tsarnaev, the public safety exception is a wise and prudent tool that federal agents can use to try and glean vital information — if the terrorist is in a mood to talk. The younger Tsarnaev is intelligent and apparently thoroughly Americanized. It is possible he knows he doesn’t have to speak to authorities anyway.

So the feds might find themselves back to square one even with the public safety exemption. As an American citizen, Tsarnaev will enter the justice system with some of the best lawyers in the country defending him. He won’t be sent to Guantanamo. He won’t be tortured. He might not even be convicted.

And sometime today, he will be read his Miranda rights and will not be under pressure to share whatever he knows, if anything, about future plots or other conspirators. It is frustrating to realize that in the age of terror, our laws and our Constitution are sometimes incapable of stretching far enough to adequately protect us.