Attorney General Eric Holder Jr. announced Thursday that the Department of Justice will investigate the Ferguson, Missouri, police department for a “pattern or practice” of civil rights violations.

The civil rights investigation is in addition to an ongoing FBI investigation into the shooting death of Michael Brown, an unarmed Black teenager who was shot and killed by Ferguson police officer Darren Wilson.

The Justice Department’s investigation will look at whether the police in Ferguson have a history of discrimination or use of excessive force beyond the Brown incident.

“In Ferguson, our investigation will assess the police department’s use of force, including deadly force,” Holder said at a press conference announcing the investigation. “It will analyze stops, searches, and arrests. And it will examine the treatment of individuals detained at Ferguson’s city jail, in addition to other potentially discriminatory policing techniques and tactics that are brought to light.”

“After the Rodney King incident and the LA riots in the early ’90s, Congress passed a law in 1994 that gives the Civil Rights Division the authority to investigate and seek relief from what are called ‘patterns or practices’ of misconduct by police departments,” explained Samuel Bagenstos, a professor of law at the University of Michigan Law School and former principal deputy assistant attorney general for civil rights in the Department of Justice from 2009 to 2011.

“What is a pattern or practice is actually a pretty common-sense term,” Bagenstos told Rewire. “It’s not just a single incident. It means there’s a general pattern of violations of the law in this police department.”

The Justice Department’s investigation, Bagenstos said, will look broadly into the conduct of the Ferguson police department to see what, if anything, about their conduct violates the Constitution: “What the Justice Department looks to when it does these investigations is, have there been a lot of incidents of police misconduct that look like constitutional violations? Maybe they are using excessive force in violation of the Fourth Amendment. Maybe they’re racial profiling in violation of the 14th Amendment. Maybe there’s violations of First Amendment rights of people to film police officers. The question is, Is there a pattern? Has this gone on for a while?”

The Justice Department’s investigation will take many months, Bagenstos explained.

“The Justice Department will send attorneys and investigators and outside experts to review incident reports from the police department, look at all the use of force reports, look at arrest records to the extent they are trying to figure out if there is a pattern of racial profiling, for example, look at tickets for the same reason,” Bagenstos said. “It’s a very labor-intensive process. It involves reading an enormous amount of documents and talking to a lot of people.”

Under Holder’s watch, the Civil Rights Division has opened 20 pattern or practice investigations into police departments across the country and prosecuted more than 300 police officers for misconduct. The Justice Department is also enforcing 14 agreements to reform law enforcement practices with agencies across the country.

“One of the things that the Justice Department has done really well in the last several years is engaging with the communities that deal with these police departments to try and find out from community members what’s going on in addition to just looking at the records in the department,” Bagenstos said.

In addition to the Ferguson investigation, the Justice Department announced it will review the St. Louis County Department’s handling of protests following the Brown shooting death and is engaging the St. Louis County Police Department in a “collaborative reform effort.”

Bagenstos explained the difference between this process and the investigation into the Ferguson Police Department: “There, Justice Department has two basic functions. One is to litigate on behalf of the United States and in the civil rights area to sue people and governments who violate civil rights. Another function of the Justice Department is to help out law enforcement agencies across the country, to give them money, technical support.”

It’s this technical support arm of the Justice Department that will be working with the St. Louis Police Department on ways police policies can be improved.

Holder explained the preliminary scope of this reform effort Thursday. “With the cooperation of St. Louis County leaders, we have identified priority areas for intensive review and technical assistance—including racial profiling; stops, searches, and frisking; the handling of mass demonstrations by police officials; and law enforcement training both at the police academy and at the continuing professional level,” Holder said.

Should investigators find evidence of a pattern of discriminatory conduct or constitutional violations, the Justice Department has the option of bringing a lawsuit against the Ferguson Police Department.

“The Justice Department does have authority to bring lawsuits against police departments that don’t cooperate and get a court order directing reform of the police department,” said Bagenstos, “although that almost never happens. It’s only when the police department is very uncooperative that you see an actual lawsuit be filed in this area.”

Instead, Justice Department officials usually resolve pattern or practice investigations through some kind of settlement agreement.

As to what types of reforms the Justice Department would be looking to institute, Bagenstos explained that will depend on what investigators find in Ferguson.

“Is the police department properly limiting and regulating the use of force by police officers so that deadly force is used only when necessary to protect the officer or to protect the public from a dangerous, fleeing felon?” Bagenstos asked. “Is there sufficient training to make sure that the police officers comply with policies like a use of force policy? Monitoring policies to make sure that when there are indications that a particular police officer is engaging in problematic conduct that the department responds in an institutional way before it gets out of hand and becomes a constitutional violation or before it happens more than once? Screening policies to make sure people who are hired are appropriate to entrust with the great power we give to police officers?”

Community activists applauded Holder’s announcement as an important first step.

“Our Ferguson area community stood united in the face of injustice and brutal repression by police who were supposed to protect and serve us,” Jamala Rogers, co-founder of the Organization for Black Struggle and organizer with HandsUpUnited, said in a statement following Holder’s announcement. “Nearly a million people joined us and signed a petition that we delivered to the White House last week demanding that the Department of Justice take real action to stop police violence, both here and across the country. When we take action together, we can make real change.”

“We commend Attorney General Holder and the Administration for hearing the voices of thousands of activists and taking action,” said Rashad Robinson, executive director of ColorOfChange, in a statement. “This is an important step, however, we know much more needs to be done in order to bring the officer who killed Mike Brown to justice and address the epidemic of deadly police violence across the country.”