Every modern police drama that has ever appeared on television has featured a scene where officers read someone their rights.  These rights became enshrined in U.S. law (and subsequently in U.S. television) after the 1966 Miranda v. Arizona Supreme Court decision.  Consequently, statements made by suspects in custody cannot be used in a trial if the statements were made without knowledge of the right to legal counsel and the right against self-incrimination.

That seems clear-cut, but in the legal world, nothing remains simple for long.  The Boston Marathon bombing has brought a wrinkle in the Miranda rights law into the public consciousness.  After Dzhokhar Tsarnaev was arrested, he was not immediately read his rights.  Instead, the Justice Department invoked the public safety exception.  This exception to Miranda comes from another Supreme Court decision regarding “a situation where concern for public safety must be paramount to adherence to the literal language of the prophylactic rules enunciated in Miranda.”  In that case, the “concern for public safety” arose from a misplaced gun.  A police officer, upon noticing that his suspect had an empty holster, asked about the location of the gun before the suspect had been Mirandized.  That question, along with the suspect’s response, was allowed at trial because the officer was addressing an imminent threat.

The Justice Department, deeming Tsarnaev an imminent threat, was similarly able to question Tsarnaev before informing him of his rights.   The public safety exception has been deployed in two similar instances: with the foiled terror plots of the Time Square bomber in 2010 and the underwear bomber in 2009.  When law enforcement did eventually inform the underwear bomber of his rights, he stopped talking (the Time Square bomber continued to answer questions after being read his rights).  Yet, what constitutes an imminent threat remains unclear.  There’s simply no litmus test for such situations.  And, as opponents to the public safety exception have noted, nothing prevents law enforcement officials from questioning suspects about an imminent threat and acting on that information prior to informing them of their rights.  Miranda simply concerns what information prosecutors can present in a trial.

Proponents of the exception argue that it allows law enforcement to quickly gather vital information while still preventing investigators from compelling suspects to make statements.  In cases where the exception has been invoked, importance has always been given to the scope of the questions–they must directly relate to the elimination of an emergency.  However, an unsigned 2011 FBI memo directed to its agents adds a further complication.  It notes that in “exceptional cases” agents may continue their interrogation beyond “all relevant public safety questions.”  Again, what constitutes an “exceptional case” is left undefined.

All of this uncertainty reveals one of the challenges of legal work. No law can adequately account for every situation.  As the public safety exception becomes more well-known and more frequently used it will also become more criticized.  Courts will have to begin refining what constitutes an exceptional case and an imminent threat, lawyers will have to apply those interpretations to particular cases, and inevitably, the public safety exception–and the debate surrounding it–will begin to evolve.