Illinois’ attorney general Tuesday called for an "outside, independent" investigation of the Chicago Police Department, questioning whether some of the department’s recent practices violated federal law.

In a letter to US Attorney General Loretta Lynch, Illinois Attorney General Lisa Madigan requested an investigation into the legality-- and constitutionality-- of the Chicago Police Department’s practices involving use of force in the wake of the release of dashcam video last month depicting the shooting death of a black teenager by a white police officer in the city in 2014.

Madigan’s office said in a statement Tuesday that a probe by the Justice Department’s Civil Rights Division is “necessary and appropriate.” The statement said a DOJ investigation would promise “an outside, independent review” of the department.

Madigan's office said the probe should consider "the adequacy of its review and investigation of officers’ use of force and investigation of allegations of misconduct; its provision of training... and whether there exists a pattern or practice of discriminatory policing."

"The shocking death of Laquan McDonald is the latest tragedy in our city that highlights serious questions about the use of unlawful and excessive force by Chicago police officers and the lack of accountability for such abuse. Trust in the Chicago Police Department is broken," Madigan said in a statement.

Protests over the contents of the video were held in Chicago last month. Chicago Officer Jason Van Dyke was charged with McDonald’s murder on November 24.

McDonald, who was carrying a knife, was allegedly shot 16 times by Van Dyke during the incident.

Earlier Tuesday, Chicago Mayor Rahm Emanuel, a Democrat, announced he had asked for and received the resignation of the city’s top cop, Superintendent Garry McCarthy.

"Now is the time for fresh eyes and leadership," Emanuel said.