The best answer is as follows. Our law rightly safeguards against convicting the innocent and tries to structure criminal trials to minimize this risk. A criminal defendant is under special emotional pressure and may end up hurting his own case, even if he is testifying truthfully. He may stutter or sweat or misremember or misspeak or get confused when verbally sliced and diced on the stand by a clever prosecutor. So at trial we don’t allow the prosecutor to force the defendant to take the stand. Likewise, we don’t allow the government to force a suspect in the police station to answer questions, and then allow those answers to be introduced at trial. Otherwise, our carefully designed safeguards could be undone pretrial, in the police station.
But as long as the precise words and testimony elicited in a police interrogation are never introduced in a criminal trial, the Fifth Amendment will never have been violated. The defendant will never have been made an involuntary witness in his own criminal case. And anything else that the interrogation leads to—bombs, guns, other physical evidence, the names of other possible witnesses or accomplices—should be fair game, because this kind of evidence is far more reliable, in general. Imagine, for example, introducing into evidence the fact that a bomb was found in a hideaway controlled by the defendant and filled with the defendant’s fingerprints.
In the 1860s, Congress passed a bill based on this understanding of the Fifth Amendment. President Lincoln promptly signed it into law—in sharp contrast to his treatment of other congressional proposals that he believed unconstitutional. Alas, the Supreme Court in the late 19th century—a malodorous era that gave us separate but equal in Plessy v. Ferguson and many other doubtful rulings—struck down the 1860s law. The Supreme Court currently demands that in general, if a person has been legally required to answer incriminating questions during a civilized interrogation, neither his answers nor any leads from these answers can be used in prosecuting him.
Not only does this misinterpretation go far beyond the letter and sprit of the Fifth Amendment, it also puts police in a special bind in a public emergency. Imagine a case—not like Boston—in which there is not much evidence of a suspect’s guilt before the police interrogation. If the police can tell a suspect that he must legally answer questions about ticking bombs and the like, they may save lives—but only at the expense of possibly handing the bad guy a get-out-of-jail-free card for his past crimes. In any future prosecution, the government will have to prove that no shred of evidence introduced was a product (or “fruit,” in legalese) of the compelled interrogation. And this can be a very hard thing for prosecutors to prove in cases in which a suspect is brought for questioning before the government has compiled an airtight case. Again, this isn’t Boston, but it’s a scenario that could easily arise.
The best solution would simply be for the Supreme Court to change course and allow the admission of all evidence gathered as a result of a civilized compulsory interrogation. Under current law, a suspect can be forced to hand over a blood sample or a fingerprint, because these items are reliable physical evidence, and they don’t violate Fifth Amendment, because blood and prints are not “witnesses,” strictly speaking, and because they are reliable in a way that pure words are not. The same logic holds for admitting all fruit and leads generated by compelled interrogation.
But even if the court won’t go that far, it should hold that in compelled interrogations involving serious and ongoing threats to public safety, evidence and leads obtained by interrogation of the suspect should always be admissible. Let’s bring coffee, donuts, and yes, lawyers, into the interrogation room. But the law should also require the suspect to answer all questions under pain of contempt—meaning he can be jailed if he refuses—and under penalty of perjury. His lawyer should understand that her job is not to aid the suspect in lying or stonewalling. Suspects will of course be tempted to lie in some situations. But even lies can often provide cues and clues to trained investigators, and interrogators should also be able to give lie-detector tests with the oversight of a judge. This is the right balance for public safety and a defendant’s rights—and the Fifth Amendment, properly understood, allows it.
Read more on Slate about the Boston Marathon bombing.