In its violent crackdowns on demonstrations since a white police officer shot 18-year-old Michael Brown in early August, Ferguson police revealed a fresh proclivity for abusing its citizens. However, the city’s finances suggest the St. Louis suburb’s criminal justice system has been stealthily exploiting residents—particularly those who are black or poor—for years.

Ferguson’s economy steadily withered over the last decade, as did its population. Yet even as the number of adult residents fell 11% between 2010 and 2013, fines collected by the city’s court system surged 85%, hitting $2.6 million last year.

That revenue stream has become an increasingly critical part of the city’s budget:

Of course, it may be that residents are simply breaking laws more frequently. But the share of arrests for petty offenses suggests something else at play.

In fact, arresting people for minor violations is exactly the point, as Brendan Roediger, professor at the Saint Louis University School of Law and supervisor of a local civil advocacy clinic, told Governing magazine in its must-read piece. “They don’t want to actually incarcerate people because it costs money, so they fine them,” Roediger said, adding that Ferguson’s court sometimes hears as many as 300 cases per hour.

If that estimate is right, this means the court is processing charges at a rate of 12 seconds per case—which sounds improbable. However, a report by ArchCity Defenders, a non-profit lawyer group, sheds some light on how that might be possible.

Note: The police department reports don’t explain why the number of arrests for outstanding warrants and traffic violations often exceeds the number of total arrests recorded. It’s possible that some of these charges aren’t counted in the total because they’re ultimately dropped.

According to the report, the Ferguson Municipal Court often starts hearing cases a half-hour before the official scheduled start time, and locks the doors five minutes after the court officially opens. Those who miss their hearing can then be charged with failing to appear, while missing court flat-out will likely result in an arrest warrant.

Though those arrested for warrant violations have a right to counsel, Ferguson and two other municipalities seldom offer any or inform defendants of this right, the ArchCity Defenders report says. If they are sentenced to probation, they often are required to pay fines that can be up to triple their monthly income. While Missouri Law requires a hearing to determine a defendant’s ability to pay, this rarely occurs, according to the report.

This practice explains why Ferguson Municipal Court issued 24,532 warrants and heard 12,018 cases in 2013. That averages out to 1.5 cases and three warrants per every household in Ferguson.

But the Ferguson police aren’t arresting just anyone for petty violations. For instance, police data reveal that officers systematically target black residents.

Though blacks make up only two-thirds of Ferguson’s population, nearly nine-tenths of vehicle stops in Ferguson involve black drivers. Those drivers are almost twice as likely as white drivers to be searched and twice as likely to be arrested. That’s despite the fact that searches of black drivers result in discovery of contraband 22% of the time, while white drivers searched by police are found to have contraband 34% of the time.

Ferguson is hardly the only area of St. Louis County embracing this cycle of petty-offense extortion, according to Governing’s calculations:

Note: Governing’s calculations are based on operating revenue; the percentage cited in the chart above refers to fines and forfeitures as a share of overall revenue.

In fact, all around the US, cash-strapped municipalities have adopted what Human Rights Watch calls the “offender-funded business model” (pdf). Courts charge fees for everything from public defenders to ”insurance policies” for community service, as this recent report (pdf) from John Jay College of Criminal Justice details. And as late-fee interest charges build up, that revenue just keeps growing.