When was the last time you heard of a grand jury decision causing a riot? Well . . . never. That's because grand juries are obscure relics of past practice, not designed to bear the full weight of a politically and symbolically important decision like the nonprosecution of police officer Darren Wilson for the death of Michael Brown in Ferguson, Missouri.
The decision by St. Louis County Chief Prosecutor Robert McCulloch to put the issue neutrally before the grand jury was intended to create a sense of public legitimacy for whatever result followed, and also no doubt to deflect blame from the prosecutor's own exercise of discretion. It failed on both counts - and with good reason.
The grand jury has its origins in a medieval English practice: the king, through his sheriff, would order a group of people to appear and report to the authorities the combination of rumor and common knowledge concerning who had committed a crime and needed punishing. The classic history of English law describes it this way: "The ancestors of our 'grand jurors' are from the first neither exactly accusers, nor exactly witnesses; they are to give voice to the common repute." The practice developed into an institution that validated accusations and therefore commenced prosecution. In the era when private individuals could bring criminal charges, the grand jury was a useful check on allegations, assuring that they had enough substance to go forward before the accused would be brought to the dock.
The Founding Fathers believed that grand juries had another use: blocking the government from bringing wildly unpopular prosecutions. In the grips of the republican spirit, the state ratifying conventions insisted on putting the grand jury into the Bill of Rights. That's why the federal government still uses them - and a big reason that roughly half the states use grand juries in some form.
Since the 18th century, however, things have changed. There are no more private criminal prosecutions. And because the grand jury hears only what prosecutors want it to hear, it no longer functions as a meaningful check on their authority. According to the maxim, prosecutors can indict a ham sandwich if they really want to do it. Protection from wrongful prosecution now belongs to the stage of the jury trial, not the grand jury.
All this background is necessary to explain why it was so strange for the prosecutors in Ferguson case to announce that they were going to present evidence to the grand jury and then let it make up its own mind. Prosecutors never treat the grand jury that way. They present a case to the grand jury only if they are actively seeking to prosecute - then they show the jury the prosecution's side of the case, and direct the jury to indict if there is probable cause to go forward.
The St. Louis County prosecutors were trying to be clever, repurposing an ancient institution for the contemporary political situation. They seemed to think that, because the grand jury members are drawn from the public, they would create public validation for whatever outcome the grand jury reached.
Yet public validation of ordinary jury trials depends on the public having heard the evidence. The Constitution provides that criminal trials be held publicly, precisely so that the citizenry knows what's going on. Grand jury proceedings are held in secret. That must've appealed to St. Louis County prosecutors, who sought to avoid a media circus. But releasing a summary of the grand jury transcripts afterward is a far cry from a public trial. Secret evidence was unlikely to produce public validation - as, in fact, it did not.
To make matters worse, the American public understands that a jury must convict beyond reasonable doubt, and that as a result, some guilty defendants are inevitably acquitted. We might not always like it, as the Rodney King verdict reminds us. But at least we understand the rules of the game.
The grand jury, on the other hand, is supposed to present a true bill based on probable cause. The standard is so low that a grand jury refusing to go forward is essentially saying that there was no plausible basis for the case in the first place.
Not having seen the evidence, we the public unsurprisingly find it shocking that the shooting of an unarmed man by a police officer should not give rise to at least the probability of a crime.
By bringing the case to the grand jury in this highly unusual way, the prosecutors were also trying to avoid taking responsibility for a decision either to prosecute or not to go forward. It's easy to understand the impulse: Prosecutors would've been criticized for either decision. What could be more appealing than putting the issue to a group of citizens and treating them as a stand-in for the public? This impulse was seriously misguided, as the riots show. The jury is not the polity - it's just a random selection of people who don't bear responsibility for enforcing the law. In the modern era, the job of law enforcement belongs to police and to prosecutors. When the police are under investigation, we need to see the prosecutors making and defending a rational decision on their own.
Prosecutorial discretion is an enormous power, as President Barack Obama recently demonstrated in another context by his executive order on immigration. To trust prosecutors with this judgment, we need to see them owning the decisions they make.
Deflecting responsibility to a grand jury can't solve the problem - and in Ferguson, it didn't.
Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard University.