City officials released hundreds of emails Thursday related to a police video that was kept secret for more than a year after a white Chicago officer shot a black teenager 16 times.

The emails, including some messages in which officials asked how they should respond to demands for the footage, were released to media outlets that have been pressing for the documents for weeks.

Mayor Rahm Emanuel and Chicago police have been under heavy scrutiny since the city, under court order, released the squad-car video last month showing officer Jason Van Dyke shooting 17-year-old Laquan McDonald in October 2014. McDonald, who was carrying a folded 3-inch knife, is seen veering away from Van Dyke in the video before the officer starts firing.

Van Dyke, who has been charged with first-degree murder, has pleaded not guilty to the charges.

The release of the video set off weeks of demonstrations and forced the resignation of Police Superintendent Garry McCarthy. It also led to an ongoing civil rights investigation of the entire Chicago Police Department by the U.S. Department of Justice. Protesters have called for Emanuel to resign.

The city released the emails a day after Emanuel said police must be better trained. His remarks came on the heels of a shooting last weekend by police that killed two people: 55-year-old Bettie Jones, who police said was shot accidentally, and 19-year-old Quintonio LeGrier, who police said was being "combative." Both were black.

Cook County State's Attorney Anita Alvarez said Thursday that she has asked the FBI for help investigating the deaths. She said the shooting "demands a very deliberate and meticulous independent investigation."

She urged the city's main police oversight agency, the Independent Police Review Authority, to perform an investigation of its own. Her office will review the results and determine if criminal charges are warranted, Alvarez said.