When a grand jury declined to indict Darren Wilson for killing Michael Brown, this did not mean that all of the legal questions had been resolved. While Wilson may not be charged with a crime under Missouri law, a federal prosecution remains possible.* “Though we have shared information with local prosecutors during the course of our investigation,” declared Attorney General Eric Holder in a statement released Tuesday, “the federal inquiry has been independent of the local one from the start, and remains so now.” And even if Darren Wilson is not charged with a state or federal criminal offense, the Department of Justice can act to make it less likely that police will shoot unarmed black men in the future.

Superficially, it might seem as if there is a good basis for charging Wilson with violating federal law. There is precedent for the federal government to step in and prosecute police officers for violent acts when local authorities are unable to secure a conviction. Most famously, two of the policemen who were caught on camera beating Rodney King but acquitted by a local jury were convicted for violating the Civil Rights Act of 1870.

As the nationwide protests that have been sparked by the grand jury no-billing the case reflect, there is certainly the possibility that Wilson’s shooting of Brown violated the latter’s civil rights. The fact that a grand jury did not even find probable cause is not necessarily dispositive. Robert P. McCulloch, the prosecutor who investigated the Brown shooting, has a long history of favoring the police. The fact that McCulloch essentially set up the grand jury to not indict Wilson and gave an oddly defensive press conference at which he sounded more like Wilson’s defense attorney than a prosecutor do not inspire confidence that justice was done.

There are, however, crucial differences between the cases. Most importantly, the King beating was captured on videotape. In the Ferguson case, the crucial question of whether Wilson reasonably believed himself to be in danger relies on inherently unreliable eyewitness testimony, some of which supports Wilson’s account and some of which doesn’t. The story that Wilson told at the grand jury was not particularly plausible, but proving that it’s false without visual evidence would not be easy. As Slate’s Jamelle Bouie explains, the police are generally given a great deal of deference by juries as well as prosecutors when they use deadly force.

So while the failure to indict Wilson seems like a classic case where failures of local law enforcement compel federal intervention, the chances of Wilson being criminally indicted are probably quite low. “Federal civil rights law imposes a high legal bar in these types of cases,” noted Holder. The Department of Justice could almost certainly secure an indictment of Wilson—it virtually never fails—but prosecutors won’t proceed unless there’s a strong likelihood of conviction. It’s not impossible that they would reach the conclusion that they have a strong chance of winning the case, but it’s unlikely.

Given the unfortunate grand jury process in Ferguson, there would be real potential value in having a trial, even if the DOJ were uncertain about the prospects of conviction. However, the DOJ generally tends to focus its resources on cases it is confident of winning. (In the context of financial fraud, one can make a good argument that they have been excessively cautious, although on civil rights Holder’s DOJ has a much stronger record.) The Supreme Court’s narrow reading of the relevant civil rights statute further complicates matters, making it harder to secure a criminal conviction.

But indicting Wilson for civil rights violations does not exhaust the possibilities of federal intervention. The Civil Rights Division of the Department of Justice is empowered by statute to file civil charges if it finds a “pattern or practice” of violating civil rights on the part of local law enforcement. The DOJ can obtain a court order or negotiate a settlement that requires changes in police practices and maintains federal supervision to ensure that the changes are implemented.

These civil interventions can be very important. “Department of Justice’s civil pattern-or-practice investigation has the potential to make a real systemic change in the way policing is done in Ferguson,” explains Samuel Bagenstos, a professor at the University of Michigan Law School who served as principal deputy assistant attorney general for civil rights under the Obama administration. “It could lead to a consent decree or other agreement that changes the way the police hire, screen, train, and monitor officers, alters use-of-force policies, and so forth. I think the pattern-or-practice cases, far more than the criminal ones, are where DOJ can make real change to policing practices.”

As Josh Voorhees argued in this virtual space earlier this year, the importance of reforming police practices in Ferguson can hardly be overstated. In a tour de force of investigative reporting for the Washington Post, Radley Balko found that the police departments in Ferguson and other small towns in St. Louis County collaborated with local courts to function in large measure as a white supremacist protection racket. Overwhelmingly white police forces impose arbitrary fines for minor legal violations on overwhelmingly African-American residents, which are often compounded by penalties for failure to appear in court or to pay fines. (The average citizen of Ferguson has three outstanding arrest warrants!) Not surprisingly, there is good evidence that these draconian enforcements are racially discriminatory.

A civil suit that leads to a settlement or court order, therefore, could ultimately be more important than a criminal prosecution. An unsuccessful attempt to convict Wilson might be worse than nothing. Even a conviction would put in prison just one unrepentant police officer. Federal action that brings real changes to systematically unjust police practices in Ferguson has the potentially to bring much greater changes than indicting Wilson would have done. The shooting of Michael Brown has drawn attention to a thick web of injustices that needs to be addressed, and the Department of Justice has the capacity to spur real change.

Correction, Nov. 26, 2014: This article originally misstated that Mike Brown may not be charged with a crime under Missouri law, though a federal prosecution remains possible. Darren Wilson may not be charged. (Return.)

Read more about Ferguson in Slate.