State and federal law enforcement agencies are engaged in an overlapping set of investigations into the killing of George Floyd. Minnesota Attorney General Keith Ellison took control of the murder prosecution from the local district attorney. And a federal criminal investigation will be conducted through the U.S. attorney’s office in Minneapolis and the Civil Rights Division in Washington, where both of us were once prosecutors.

Both investigations are important for delivering justice. But there is a third type of investigation that would help reform the Minneapolis Police Department overall, rather than only focusing on a few bad actors. This kind of investigation — called a “pattern or practice” investigation — has proved successful in police departments across the country. Unfortunately, U.S. Attorney General William P. Barr refuses to open one in Minneapolis, and the Trump administration has all but abandoned them.

Congress created the authority for these federal investigations, formally known as 34 U.S.C. § 12601, in the aftermath of the vicious beating of Rodney King by LAPD officers. The four officers were tried and acquitted in 1992. The failed local prosecution led to riots — but it was followed by a successful federal prosecution, which convicted two of the officers of federal civil rights violations. But even that victory couldn’t fix a Los Angeles Police Department that had been exposed as racist, frequently trampling on the civil rights of black and brown Angelenos. So Congress enacted Section 12601 as part of the 1994 crime bill. Although that crime bill is rightly criticized for many things — expanding the death penalty and life sentences, curtailing parole and providing huge sums of money to build new prisons — the creation of “pattern or practice” authority is one of the things it did right.

Pattern or practice investigations are civil, not criminal, investigations, and they aim at systemic problems, not individual officers. They allow the federal government to sue any law enforcement entity that engages in “a pattern or practice of conduct … that deprives persons of rights, privileges, or immunities secured or protected by the Constitution or laws of the United States.”

The government cannot sue for money, but it can sue for what’s called equitable and declaratory relief, which is an order from a judge that police agencies have to enact specific reforms. Most cases don’t go to trial. Once the federal government has uncovered specific and multiple constitutional violations, the police department will often begin negotiating rather than defend its practices in court. These usually result in “consent decrees,” where the police departments agree to reform their practices. The LAPD was the subject of one of the first major consent decrees, which lasted from 2001 to 2013.

While public attention may be drawn to a police department because of a horrific event like the King beating, there’s no such thing as a consent decree for a single bad action. The federal government doesn’t seek a decree unless its investigation shows systemic misconduct.

A more recent example came in Chicago, after the 2014 killing of Laquan McDonald by Chicago Police Officer Jason Van Dyke. In their initial police reports, officers falsely claimed that McDonald was lunging at them with a knife. After significant public agitation and investigative journalism, a video was later released that showed that McDonald was actually walking away when Van Dyke shot him, and that Van Dyke continued to shoot him as he was lying on the ground. Van Dyke was charged by the state and convicted of second-degree murder.

But that criminal prosecution did not address a culture that allowed numerous officers working alongside Van Dyke to cover for him. Nor did it address the years of excessive force in Chicago that preceded McDonald’s murder or the broken accountability systems that allowed police brutality to go unchecked. To get at those entrenched problems, the Justice Department opened an investigation under its “pattern or practice” authority.

In investigations like these, the federal government sends attorneys and investigators to the city to learn as much as it can about the areas of police conduct under scrutiny — such as the use of force, stops and searches, suppression of free speech or all of the above. The team interviews officers and reviews arrest reports, citizen complaints, department policies and training materials. They also hold community forums and interview residents about their interactions with police to gather evidence from across the community. With the help of data scientists and experts with law enforcement backgrounds, they assess whether there is a pattern of unconstitutional conduct and also identify the sources of the systemic misconduct, such as the failure of accountability systems or the adoption of harmful policing strategies like “broken windows” or “zero-tolerance” approaches.

The investigations are intensive and extensive: The one in Chicago took a year and involved interviews with 340 members of the police department. (One of us, Chiraag Bains, worked in the Civil Rights Division’s front office at the time and helped review the Chicago findings letter after the investigation was finished.)

During the Obama administration, the Justice Department routinely made its findings public in detailed reports. In Chicago, the department issued a report — called a findings letter — explaining that the police department had “engage[d] in a pattern or practice of using force, including deadly force, that is unreasonable,” and that it had “not provided officers with adequate guidance to understand how and when they may use force, or how to safely and effectively control and resolve encounters to reduce the need to use force.”

A findings letter like that, which showed a clear pattern of constitutional violations, would normally tee up a lawsuit where the federal government would seek structural reform.

The negotiation process is hard-fought, but it results in a set of reforms that both sides believe are feasible to implement and strong enough to correct the problems. The agreements typically include some common elements: stricter rules on when police can use force, policies to prevent discrimination, better training and data collection, fairer hiring and promotion processes, stronger accountability systems for misconduct and mechanisms for community influence over department policy.

Once the consent decree is agreed to, the court has the authority to monitor its implementation. If the city doesn’t comply, it can be held in contempt and sanctioned through fines or additional requirements.

There is strong evidence that consent decrees work. According to one study, departments that went through consent decrees saw an average of 25 percent fewer police shootings in the first year of implementation. In Detroit, police shootings dropped from 47 in the five years before the consent decree to 17 in the five years after. From 2011 to 2019, serious use of force declined 63 percent in Seattle, which entered a consent decree in 2012. Most decrees have data collection and analysis requirements, so the community can see whether force, misconduct and racial disparities are decreasing. They are not a complete solution, but they make a difference.

But in Chicago, the process froze right after the Justice Department issued its report. One of the most important aspects of that findings letter turned out to be its date: Jan. 13, 2017, one week before President Trump entered office.

Trump’s Justice Department not only refused to act on the report, but it actually weighed in against the Illinois attorney general when she sought a consent decree under state authority. Once Trump took office, his administration moved immediately to stifle the pattern or practice program, attempting to back out of an agreement in Baltimore and ordering a full review of all police reform cases. The day before Trump fired him, Attorney General Jeff Sessions issued new guidance that severely restricted the use and duration of consent decrees. Trump’s Justice Department has opened just one narrow investigation focusing on a single unit of the Springfield Police Department in Massachusetts, compared with 25 under President Barack Obama.

The career employees who work on consent decrees remain as dedicated and professional as ever — we have worked alongside them and have seen it firsthand. But their unit has atrophied to half its size since Trump took office. And the big-picture decisions are not made by those attorneys; they are made by political appointees. Without their support, the investigations won’t happen, or they won’t have teeth if they do.

Even some Republican politicians are beginning to realize that this is a mistake. Sen. Roy Blunt (R-Mo.) said last week that he would ask Barr to bring “pattern or practice” investigations back.

With the federal government missing in action, Minnesota’s Department of Human Rights announced June 2 that it will investigate whether the Minneapolis Police Department has engaged in systemic discrimination over the past 10 years. And on Sunday, a majority of the Minneapolis City Council announced that it would “begin the process of ending the Minneapolis Police Department and creating a new transformative model for cultivating safety in our city.”

But for now, the Minneapolis Police Department exists and is badly in need of intervention, and the 17,000 law enforcement entities across the country need a watchdog. There is no replacement for a federal government with deep experience in police reform. The tools are there. We just need a Justice Department willing to use them.