"What we are looking at is whether or not the police department has engaged in unconstitutional policing," Lynch said in announcing the investigation, which she said had been requested by several officials and activists.
The probe will be handled by the department's Civil Rights Division and the U.S. Attorney General's Office for the Northern District of Illinois. It will particularly look into the use of deathly force and the accountability systems in place at the Chicago Police Department, including disciplinary actions and the department's response to complaints of misconduct.
Chicago Mayor Rahm Emanuel welcomed the investigation, pledging the city's full cooperation.
"Our mutual goal is to create a stronger, better Police Department that keeps the community safe while respecting the civil rights of every Chicagoan," Emanuel said in a statement today. "Nothing is more important to me than the safety and well-being of our residents and ensuring that the men and women of our Police Department have the tools, resources and training they need to be effective crime fighters, stay safe, and build community trust."
There's no set timeline for the investigation, which Lynch said is "in the interest of the people of Chicago, who deserve a world-class police department and constitutional policing."
Hours after Lynch's announcement, Emanuel also appointed Sharon Fairley to head the Independent Police Review Authority after its former director, Scott Ando, resigned Sunday.
During a news conference this afternoon, Fairley said she brings "no agenda other than the pursuit of integrity."
Fairley's appointment is the latest in a series of measures Emanuel has implemented since the McDonald case put the city, and several politicians, in turmoil. An expansion of the use of body cameras by police officers and the creation of a task force to examine and promote police accountability round up the mayor's push to quell discontent at police in the city.
Lynch's announcement comes exactly one week after Illinois Attorney General Lisa Madigan sent a letter to the Department of Justice last week asking it to investigate Chicago police. Madigan said then that the McDonald case "highlights serious questions about the use of unlawful and excessive force by Chicago police officers and the lack of accountability for such abuse," according to a statement.
Lynch said building trust is one of the goals of opening the investigation/
"When suspicion and hostility are allowed to fester, they can build unrest," she said.
Chicago police have been under scrutiny since the video, which appears to show Van Dyke shooting McDonald 16 times, was made public on Nov. 24. Van Dyke is charged with first-degree murder, for which he pleaded not guilty.
But Emanuel has also been shrouded in controversy. He and Cook County State's Attorney Anita Alvarez have had to dismiss calls for their resignations amid lingering discontent on how the city handled the McDonald case. Alvarez has come under fire for taking 400 days after McDonald's shooting to file charges against Van Dyke and keeping dash-cam video of the shooting under wraps until a court ordered its release.
In announcing McCarthy's resignation, Emanuel said he had formed a five-person task force to oversee police accountability. The group will work to improve the independent oversight of police misconduct, deal with officers with repeated complaints and recommend the release of videos of police-involved incidents.