By Ian Millhiser on Apr 19, 2013 at 10:34 pm | ThinkProgress

Despite initial reports to the contrary, FBI agents did not read Boston Bombing suspect Dzhokhar Tsarnaev his Miranda rights immediately after he was taken into custody. Instead, they invoked what is known as the “public safety exception” to delay reading those rights to the alleged bomber. Here’s what you need to know about this narrow exception to the Miranda rule:

The Public Safety Exemption Is Real

The Supreme Court first held that there is a public safety exemption to Miranda in a 1984 case known as New York v. Quarles. In Quarles a woman told police that a man with a gun raped her, and that he’d run into a nearby grocery store. Police quickly found the suspect within the store, arrested him after a brief chase, handcuffed him, and discovered that he was wearing an empty shoulder holster. Before reading him his rights, an officer asked him where the gun was, and the suspect told the cop where to find it. After retrieving the gun, police then read the suspect his Miranda rights.

Although the Constitution generally forbids law enforcement from interrogating suspects in custody without first reading them their rights, the Court held that a narrow “public safety exemption” permitted the limited questioning that occurred in Quarles. As the Court explained, “procedural safeguards which deter a suspect from responding were deemed acceptable in Miranda in order to protect the Fifth Amendment privilege; when the primary social cost of those added protections is the possibility of fewer convictions, the Miranda majority was willing to bear that cost. Here, had Miranda warnings deterred Quarles from responding to Officer Kraft’s question about the whereabouts of the gun, the cost would have been something more than merely the failure to obtain evidence useful in convicting Quarles. Officer Kraft needed an answer to his question not simply to make his case against Quarles but to insure that further danger to the public did not result from the concealment of the gun in a public area.”

As the Court emphasized, this exemption is “narrow.” It permits police to ask a limited range of questions for the purpose of removing any imminent threats. It does not permit wide-ranging questions intended to build a case against the suspect.

FBI Guidelines Apply The Public Safety Exemption Aggressively In Terrorism Cases

A 2011 FBI memorandum says agents may delay reading Miranda rights to a suspect in “exceptional cases” when the FBI “conclude[s] that continued unwarned interrogation is necessary to collect valuable and timely intelligence not related to any immediate threat.” According to a DOJ spokesperson, this guidance exists because “the threat posed by terrorist organizations and the nature of their attacks—which can include multiple accomplices and interconnected plots—creates fundamentally different public safety concerns than traditional criminal cases.” Needless to say, this guidance is controversial, as it extends the public safety exemption beyond truly imminent threats to encompass more distant — but also potentially more deadly — future threats.

In any event, it is worth emphasizing again that the public safety exemption does not allow broad ranging questions for the purpose of building a criminal case. Even if the Obama Administration is correct that the exemption can be applied more broadly to suspected terrorists, law enforcement may only invoke the exemption to ask “questions necessary to secure their own safety or the safety of the....”

The FBI Cannot Indefinitely Delay Reading Tsarnaev His Miranda Rights

Because the public safety exemption is rooted in the “need for answers to questions in a situation posing a threat to the public safety,” it is only temporary. Eventually, it may become clear that no such threats exist (or at least any that Tsarnaev is capable of providing information about). At that point, he must be read his Miranda rights even under the most lax plausible understanding of the exemption. Additionally, if law enforcement wishes to ask Tsarnaev questions geared towards gathering evidence to use against him at trial, they must read him his Miranda rights.