U.S. Attorney General Loretta Lynch, seen here making a statement last week, announced an investigation into the Chicago Police Department Monday. Getty Images

UPDATE: 10:43 a.m. EST -- Chicago Mayor Rahm Emanuel tweeted a statement supporting Attorney General Loretta Lynch's decision to investigate the city's police department. "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," he wrote.

Original story:

Announcing a Department of Justice investigation into the Chicago Police Department Monday, Attorney General Loretta Lynch said Monday that Americans deserve "effective, responsive, respectful, and most importantly, constitutional" protection by law enforcement. When they don't, and instead feel ignored or mistreated, she said there are "profound consequences" for the well-being of communities and their police officers.

Lynch said the probe would determine whether the Chicago Police Department had systematically violated the Constitution or federal law. The inquiry will focus on the police department's use of force, deadly force and accountability, specifically examining racial, ethnic and other disparities, how the department handles allegations of excessive force and how officers are disciplined after misconduct.

"Our goal in this investigation – as in all of our pattern-or-practice investigations – is not to focus on individuals, but to improve systems; 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," Lynch said in a statement. The Justice Department recently started similar inquiries into police operations in Ferguson, Missouri, and Baltimore, Maryland, both scenes of fatal police shootings of black men.

The announcement came about two weeks after a judge ruled that officials had to release a video showing the fatal police shooting of Laquan McDonald, a 17-year-old killed in October 2014. The police department had issued a statement saying McDonald approached its officers with a knife, but the video appears to show him walking away from the police, who kept firing once he fell to the ground, the Huffington Post reported. The officer in question, Jason Van Dyke, has been charged with murder, and police Superintendent Garry McCarthy was asked to resign. Meanwhile, critics accused Mayor Rahm Emanuel of covering up the incident for political gain.

Lynch did not discuss details of the McDonald case, only saying that the federal investigation was ongoing. She said she didn't know what the Chicago probe's timeline looked like.