The DOJ investigation is the largest ever into a city law enforcement department.

The Justice Department will investigate the Chicago police for possible civil rights violations, Attorney General Loretta Lynch announced Monday morning.

Later Monday, NBC and CBS reported that Constantine "Dean" Andrews, the Chicago Police Department's chief of detectives, had resigned from his post.

As the second largest force in the nation, Chicago's will be the biggest city department the Attorney General's office has ever investigated (Puerto Rico's was the largest one overall).

The investigation will focus on the racial and ethnic disparities involving the CPD’s use of force, use of deadly force and its's systems of accountability, Lynch said.

"Our goal in this investigation, as in all of our pattern-or-practice investigations, is not to focus on individuals, but to improve systems," Lynch said. "To ensure that officers are being provided with the tools they need -- including training, policy guidance and equipment -- to be more effective, to partner with civilians and to strengthen public safety."

Illinois Attorney General Lisa Madigan wrote to Lynch Dec. 1 to urgently request an investigation into the police department. Madigan asked the DOJ to investigate whether the department's use of force and racial disparity issues amount to civil rights violations.

Madigan's call for the DOJ probe came just days after a court order forced the city of Chicago to release dashboard camera footage of a 2014 fatal shooting that involved police. The video shows 17-year-old Laquan McDonald walking away from police before he is shot 16 times.

The FBI, the Justice Department and the Independent Police Review Authority are all reviewing the McDonald case, including claims that police tampered with surveillance video from a nearby Burger King restaurant that captured the shooting.

Attorney General Loretta Lynch, left, and U.S. Attorney in Chicago Zachary Fardon, at a news conference at the Justice Department in Washington D.C. on Monday.
Attorney General Loretta Lynch, left, and U.S. Attorney in Chicago Zachary Fardon, at a news conference at the Justice Department in Washington D.C. on Monday.

The department will release a report of the findings at the end and if necessary, compel the CPD and the City of Chicago to address constitutional violations through a court motion.

Neither Lynch nor her deputy, Vanita Gupta, could say how long the investigation into the roughly 12,000-person police force is expected to take.

A 2012 federal investigation into excessive force by the roughly 1,500-person Cleveland Police Department took 18 months to complete. Lynch rejected concerns that an investigation into a department the size of Chicago would stretch beyond her tenure in President Barack Obama's administration.

Chicago's massive police force has an equally robust history of misconduct that stretches back nearly a century. Lynch would not specify how far back she would go in her investigation.

"Regardless of the findings in this investigation, we will seek to work with local officials, residents and law enforcement officers alike to ensure that the people of Chicago have the world-class police department they deserve," Lynch said.

Gupta promised that the Civil Rights Division investigation would be thorough and "leave no stone unturned."

Chicago Mayor Rahm Emanuel, who originally resisted the notion of a federal probe, said in a statement Monday that he welcomed the DOJ's investigation and pledged the city's "complete cooperation."

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