US Attorney General Announces Justice Department Probe Into Chicago Police

Less than a week after Chicago Mayor Rahm Emanuel asked his top cop to step down, US Attorney General Loretta Lynch announced on Monday that her department has launched an investigation into the city's entire police department.

The announcement follows ongoing protests over the fatal police shooting of black 17-year-old Laquan McDonald last October, as well as allegations earlier this year that Chicago police used abusive interrogation techniques on detainees held at a "black site" warehouse in the city.

Lynch said that the investigation into the department's "patterns and practices" will focus on the use of excessive and deadly force, racial bias, and systems of accountability to determine whether its officers systematically violate constitutional rights.

Related: Chicago Police Chief Garry McCarthy Fired in Wake of Laquan McDonald Video

"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," she said. "This mistrust from members of the community makes it more difficult to gain help with investigations, to encourage victims and witnesses of crimes to speak up, and to fulfill the most basic responsibilities of public safety officials. And when suspicion and hostility is allowed to fester, it can erupt into unrest."

The probe comes amid protests sparked by dashcam video footage of McDonald's death. On the day the footage was released, Officer Jason Van Dyke, who shot the teen 16 times in the middle of a street, was charged with murder. The demonstrations have largely focused on why it took over a year for the footage to become public and charges to be filed, and led Emanuel to essentially fire Police Superintendent Garry McCarthy on Tuesday.

Adam Collins, a spokesperson for Emanuel, said Sunday that his office welcomes the probe.

"We welcome the engagement of the Department of Justice as we work to restore trust in our police department and improve our system of police accountability," he said.

Related: Protesters Denounce Detainment and Abuse at Alleged Chicago Police 'Black Site'

The release of the video comes at a time of heightened debate in the United States over police use of lethal force, especially against black people. Over the past year, protests over the issue have rocked a number of US cities.

A patterns and practices investigation does not criminally charge individuals, but often results in a consent decree between a police department and the Justice Department to agree to new practices and accountability measures.

In May, the DoJ launched an investigation into the Baltimore Police Department's use of force and whether there were patterns of discriminatory policing after the death of Freddie Gray, a 25-year-old black man, who suffered fatal injuries while in police custody. The Justice Department also recently investigated police in Ferguson, Missouri, where a white officer fatally shot an unarmed black teenager last year, concluding in March that the department routinely engaged in racially biased practices.