Proceedings in Florida's case against George Zimmerman for the tragic shooting death of Trayvon Martin have recently provided an object lesson in how the institution of bail is supposed to work — but almost never does.

Last week, George Zimmerman's wife was charged with perjury for lying at her husband's bail hearing in April — she testified that the couple was broke, which prompted the court to set a low bond. But since then prosecutors have alleged that, at the time of the hearing, the Zimmermans had in fact raised over $100,000 for the defense. The court responded by revoking the defendant's bail.

All of this attention to the Zimmermans' financial means is necessary if the court is going to get a bail determination right. Unfortunately, bail is almost always pegged exclusively to the crime charged, which gets the law of bail wrong, with injustice often the result.

"Bail" is the security a defendant posts to remain at liberty before trial. Historically, the institution of bail is meant to ensure that the defendant put at risk of forfeit enough money to ensure his appearance in court. That purpose is enshrined in the law of every state that still uses bail. In recent years, some states, Maryland included, have added an additional purpose to bail — namely, that the defendant put up enough money to dissuade him from endangering the community.

But whatever its purpose, bail amounts must be measured in part by a defendant's means. Maryland law requires that pretrial conditions be the "least onerous" necessary. For money bail, that means the minimum amount necessary to ensure the defendant returns to court and stays out of trouble. A bail amount out of the defendant's reach isn't bail at all — it's simply a backhanded way of locking someone up.

But instead of inquiring into the defendant's means, the focus is often narrowly on the alleged offense and the defendant's criminal history. In its 2011 study of Maryland bail practices, The Abell Foundation reported that district court commissioners "often lack" critical information about "the defendant's employment status or financial ability to afford a money bail," and the majority of them did not even view such information as important. The report serves to confirm what courthouse regulars in every state know: bail is primarily a function of the crime charged.

In contrast, there is little incentive to consider a defendant's means. Dockets are crowded; defense lawyers, even when present, are overburdened. There is a strong incentive to keep things moving.

Considering the severity of the offense is not irrational, of course; it is plainly related both to the likelihood of flight and to a defendant's dangerousness. The problem is that state court systems tend to elevate the charged offense to the primary or even sole consideration.

As it currently operates, this system distorts the institution of bail. For a defendant who can actually scrape together no more than, say, a thousand dollars, what justification is there for setting bail far in excess of that amount? For such a defendant, bail above $1,000 means he will remain in jail, period. It does not mean the court has determined how much is necessary to keep him in town, or out of trouble, until trial.

Courts do get bail right, of course, but mainly in high profile cases like Mr. Zimmerman's, or cases in which well paid defense counsel have more time and resources. Yet figuring out the amount of money to which a person has access is not a rare or mysterious process. It happens every day, whenever someone applies for an auto loan or a credit card or financial aid. The law governing bail would seem to demand no less.

If proper bail hearings are prohibitively expensive or time-consuming, it's worth considering the alternatives. The District of Columbia, for example, has abandoned it. Courts have an expanding set of tools — such as travel restrictions and electronic monitoring — all of which seem more directly related to keeping defendants close than the numerology of guessing what sum of money is just enough to keep them from fleeing or causing harm.

Before finding someone guilty, the rules of criminal procedure require a hugely costly trial. Bail deprives people of their freedom no less than a post-trial sentence, but with the barest minimum of inquiry. A free society should do better.

Barton Aronson

The writer is a former federal and state prosecutor.