WHEN America faces an immensely important question with dramatic racial and social overtones like whether the shooting death of an unarmed black teenager in Florida was murder or self-defence, we have an established way of handling it: we pluck a bunch of random people with no special legal training off the street, make them listen to two heavily biased and diametrically opposed versions of the evidence for a few weeks, and then abide by whatever decision they make. This isn't necessarily a crazy way to handle the process; we and other countries that share our legal heritage have been using it for centuries, so it's clearly workable, at a minimum. But you have to admit it's kind of weird. People who come from countries that use Napoleonic-style systems of investigating magistrates often find the idea of having their guilt decided by an arbitrary collection of six or twelve of their fellow citizens discomfiting.

That said, it's not immediately clear that being tried by independent legal experts is any better. Functionaries ensconced in the judicial system may be more susceptible to "capture" by the police or prosecutors, or simply to developing consistent organisational biases they can't even recognise. There probably isn't any truly unbiased way to decide whether people are guilty of murder, in a fashion that eliminates social prejudice. The role of trial-by-jury in cases iike the acquittal of George Zimmerman on the charge of murdering Trayvon Martin boils down to two questions.

1. Are juries racially biased? Of course they are. Economists Shamena Anwar of Carnegie Mellon, Patrick Bayer of Duke, and Randi Hjalmarsson of Queen Mary University studied Florida jury verdicts from 2000-2010; they found that "(i) juries formed from all-white jury pools convict black defendants significantly (16 percentage points) more often than white defendants and (ii) this gap in conviction rates is entirely eliminated when the jury pool includes at least one black member." However, the non-jury "professional" elements of the American justice system may be even more racially biased. Last year John Roman of the Urban Institute crunched the data on "justifiable homicide" determinations broken down by race and by whether or not the state was a stand-your-ground state. These are determinations made by police or prosecutors as to whether a homicide was justifiable, before the case ever reaches a jury trial. He found that white-on-black killings were more than twice as likely to be found "justified" as white-on-white killings, and more than three times as likely in stand-your-ground states. And of course it was the trained law enforcement professionals in the police force, not any jury, that initially decided George Zimmerman should not even be arrested for the killing.

2. Are non-jury judicial systems less racially biased? I'm not sure there's much reason to believe this is the case. The Netherlands, for example, uses a system of "politierechters", or police judges, for less serious criminal offences such as theft, fraud and assault. A study published last year by three University of Leiden criminologists of 365 trials at 10 Dutch courts found that "Dutch-looking" Dutch citizens received jail sentences for such offences 11% of the time. "Foreign-looking" Dutch citizens, generally those who appeared to have Middle-Eastern, black, or eastern-European ancestry, received jail sentences 28% of the time. (Actual foreigners who did not speak Dutch received jail sentences more than half the time.) I haven't been able to quickly hunt up any studies of racial bias in non-jury trials in Germany but I would be surprised if it were any less pronounced than in the Netherlands. And in France a murder felony like the Zimmerman case would probably get a form of jury trial as well.

If we look at the evidence, I don't think there's any reason to think that getting rid of trial by jury would reduce racial bias. But in an impressionistic narrative fashion, the jury angle does seem to be an elemental part of it. America has trial by jury because this quaint throwback to a medieval judicial system survived Britain's gradual transition to modernity, whereas in continental Europe it was mostly swept aside by Napoleonic and Bismarckian reforms. The decentralised medieval institution then adapted itself to the setting of a pioneer state with high (medieval, even) levels of violent crime, where a settler majority was pursuing brutal programmes of racial oppression and conquest. Trial by jury was used by local communities to wink at violence carried out by whites in establishing or defending local hegemony over native Americans and blacks; such permission for ethnic violence might have been less forthcoming from regular government magistrates following clear regulations. The impunity granted by sympathetic juries maps to the vigilantism of informal "posses" as instruments of irregular violence practiced by whites in establishing frontier America's racial order.*

Of course there is no American frontier anymore. But we cannot seem to stop imagining we are still there. What did George Zimmerman imagine he was doing, running around a Florida subdivision in the middle of the night with a gun? Whatever it was, it seems he could still count on the same bedrock commitment that vigilantes in America have reckoned on since the days of Indian reprisals and escaped slaves: no jury would ever convict him.

* By the time I figured out a clearer way of saying what I was trying to say here, I'd published the post, so instead I'm going to amend that clearer point here. The point is this: juries are intended as a check on judicial power, and that is in fact the way they function. What that means is that they tend to acquit defendants whom judges, acting alone, would convict. From the first major study on juries in the 1950s ("The American Jury" by Harry Kalven and Hans Zeisel) down to today, the evidence is that juries pretty much acquit the same defendants judges would acquit, and also acquit some people the judges would have convicted. The familiar phenomenon we've seen throughout US history is that when an ethnic majority is practicing violence against a minority, the fact that juries are more likely to acquit defendants becomes a useful tool. After all, only 2% of criminal cases ever get to a jury trial; in most cases the state uses its power to pressure the defendant into a plea bargain. The cases that do go to a jury are likely to be those where the accused either dramatically misjudges their situation, or has access to the resources needed to mount a strong defence, either because they are personally wealthy (O.J. Simpson) or because they can draw support from sympathisers in their own ethnic community (George Zimmerman). If the acquittal of George Zimmerman has a bit of the feel of those old cases from America's red-in-tooth-and-claw history, this is probably part of the reason.