Attorney General Loretta Lynch announced on Dec. 7 the Justice Department will investigate the Chicago Police Department for possible "patterns and practices" violations. The Post's Wesley Lowery explains what that actually means. (Gillian Brockell/The Washington Post)

The Justice Department will investigate the Chicago Police Department to see whether the force “has engaged in a pattern or practice of violation of the Constitution or federal law,” Attorney General Loretta E. Lynch announced Monday.

“Our investigation is focused on use of force and the accountability within the police department,” Lynch said.

The probe follows similar federal civil rights investigations that were launched in Ferguson, Mo., and Baltimore, in the wake of unrest in both cities. In Chicago, federal investigators will look at how officers use deadly force and examine any racial or ethnic disparities in how force is employed, as well as how the department handles discipline and allegations of misconduct.

This investigation into the country’s second-largest local police department comes less than two weeks after the Chicago force came under the national spotlight because of recently released video footage showing a white police officer fatally shooting a black teenager. The Washington Post first reported Sunday that the Justice Department would open this investigation, putting Mayor Rahm Emanuel’s force under the microscope of his former colleagues in the Obama administration.

[Prosecutors say no criminal charges against Chicago police officer who fatally shot Ronald Johnson]

Attorneys from the Justice Department’s civil rights division will meet with officers, law enforcement command, city officials and other community members, Lynch said. If the investigation finds any unconstitutional behavior, federal officials would work with the city to enact reforms, something the attorney general noted would come with a court-enforced agreement.

“We understand that the same systems that fail community members also fail conscientious officers by creating mistrust between law enforcement and the citizens they are sworn to serve and protect,” Lynch said.

The intense scrutiny of the Chicago police stems from the October 2014 death of Laquan McDonald, a black 17-year-old. Although McDonald’s death occurred more than a year ago, it was only last month that authorities, acting on a judge’s order, released footage of Officer Jason Van Dyke shooting the teenager. Van Dyke was charged with murder the same day that video footage was released.

[Why did authorities say Laquan McDonald lunged at Chicago police officers?]

In the video clip, captured by a dashboard camera, Van Dyke is seen firing a volley of shots at McDonald, many of them after the teenager had fallen to the ground. And though the initial accounts from authorities suggested that McDonald was approaching officers, the video showed him appearing to veer away before he was shot.

City officials agreed earlier this year to pay McDonald’s family $5 million in a settlement. But they fought releasing the video footage of the shooting, arguing that it would impede ongoing investigations into the incident.

[Judge: Chicago police must notify media before destroying decades of misconduct files]

In the days after the video was released, anger erupted on Chicago’s streets, with peaceful protests stretching through downtown streets. Activists have railed against the police department and the long lag between McDonald’s shooting and the announcement last month that the officer involved would be charged.

A separate federal investigation into the McDonald shooting is ongoing.

Less than a week after the release of the video, Emanuel, a Democrat narrowly reelected to a second term earlier this year after being forced into an unexpected runoff, dismissed the head of the police department. He also announced a new task force that would look at ways to improve police accountability.

The same day that Emanuel fired Garry F. McCarthy, the police superintendent, Illinois Attorney General Lisa Madigan asked the Justice Department to investigate possible civil rights violations by the Chicago Police Department. In her letter, Madigan described trust in the police as “broken, especially in communities of color,” and cited several cases of officers in Chicago shooting people in the city.

Emanuel had called a federal civil rights investigation “misguided,” but he reversed course last week and said he would welcome it. On Monday, Emanuel pledged “complete cooperation” with the federal investigation.

“This is not the end of the problem but the beginning of a solution,” he said. He added: “This is bigger than one particular incident. We need comprehensive solutions to address the systematic challenges that exist in the Chicago Police Department.”

The Justice Department’s decision to investigate the broader practices of the Chicago police comes amid a widespread focus on how officers use deadly force against black men and boys. High-profile incidents across the country have sparked protests and unrest, and police officers have described feeling increasingly tense and say they feel demonized.

Federal investigators have probed a host of departments in recent years, looking at forces in Cleveland; Seattle; New Orleans; Portland, Ore.; and Albuquerque. In 1994, Congress empowered the Justice Department to look at — and force — systemic changes in local police departments, and in some cases courts approved and managed binding reform agreements. These federal investigations can drag on for years and cost hundreds of millions of dollars.

The report on the police force in Ferguson, released earlier this year, said officers there routinely violated the constitutional rights of black citizens. A probe into the Baltimore police force, requested by that city’s mayor, was launched in May.

Related:

The Post’s database on police shootings

How The Post is tracking these shootings

Unarmed and Black: unarmed black men are seven times more likely than whites to die by police gunfire

Current and former police officers describe tension in current environment

[This post has been updated. First published: 10:10 a.m.]