The U.S. Justice Department has started an investigation into the "pattern and practice" of the Chicago Police Department to determine whether it violated the constitution or federal law with its handling of use of force.
The probe follows the release of a video last month showing the shooting death of a 17-year-old by a police officer in October 2014.
"Every American expects and deserves the protection of law enforcement that is effective, that is responsive, that is respectful, and most importantly constitutional," said Attorney General Loretta Lynch in announcing the investigation Monday.
"We will examine a number of issues related to the Chicago Police Department's use of force, including its use of deadly force, racial, ethnic and other and disparities in its use of force and its accountability mechanisms — such as disciplinary actions and its allegations of misconduct," she said.
Chicago police Officer Jason Van Dyke was charged with first-degree murder Nov. 24, more than a year after the killing of Laquan McDonald and just hours before the release of police dashboard camera footage showing the officer shooting the black teenager. The dashcam video shows McDonald jogging toward police, and then he appears to be walking away from police as he's shot 16 times, many bullets hitting him after he falls to the ground.
Protests started that night in Chicago, claiming a police department cover-up. They continue periodically. Chicago Mayor Rahm Emanuel fired the city's police superintendent last week. Demonstrators also are calling for the outster of the Chicago prosecutor and Emanuel himself.
Chicago police Officer Jason Van Dyke, left, and Laquan McDonald.
Lynch said if any actions of the department are found unconstitutional, the agency will enter into a court agreement with the police department and also work with the city of Chicago on reforms.
She said the investigation will focus on improving systems, not pointing out offending individuals.
Hours after Lynch's announcement, State's Attorney Anita Alvarez gave a detailed presentation to reporters explaining why she would not seek charges in another 2014 police shooting death of a black man.
Alvarez on Monday released a dashcam video that shows 25-year-old Ronald Johnson running from police across a street with several officers in pursuit, and then one officer shooting. Johnson is not on screen when he was struck by two bullets.
The video also was slowed down to show what prosecutors said was a gun in Johnson's hand.
Experts say some communities increasingly do not feel they are getting the kind of policing they should.
Lenese Herbert, a law professor at Howard University in Washington, said she remains concerned about not just upholding "the letter of the law, but the spirit of the law," though she said she thinks the Justice Department probe is a good first step.
"Sunshine is the best disinfectant," she said. "We need this opening up and understanding the situation in great detail."
Similar Justice Department investigations were held after protests in Baltimore, Maryland, and Ferguson, Missouri, following police involvement in the deaths of African-American suspects.
In April, a 25-year-old suspect died after being transported to the Baltimore City jail. The trial of the first Baltimore police officer accused in the death of Freddie Gray is now underway.
In Ferguson, Missouri, last year, an 18-year-old African-American robbery suspect was shot by a white police officer, sparking days of unrest, some violent. That was especially true following announcements by the grand jury and the justice department that Ferguson police officer Darren Wilson would not be charged in the shooting.