CHICAGO - Mayor Rahm Emanuel announced Tuesday that he had dismissed Chicago Police Superintendent Garry McCarthy, citing a lack of public trust in police leadership after a high-profile shooting that led to a white officer's being charged with first-degree murder in the death of a black teen who was shot 16 times last year.

"Superintendent McCarthy knows that a police officer is only as effective as when he has the trust of those he serves," Emanuel said at a City Hall news conference, where he appointed a task force to look at police accountability.

Emanuel said he and McCarthy began discussing the future of the department Sunday, and "the undeniable fact that the public trust in the leadership of the department has been shaken and eroded."

"This morning, I formally asked for his resignation," said Emanuel, who said McCarthy could be proud of his record. "Now is the time for fresh eyes and new leadership to confront the challenges the department and our community and our city are facing as we go forward."

Emanuel said he had asked new First Deputy Superintendent John Escalante to serve as acting superintendent during a "thorough" search.

"This is not the end of the problem, but it is the beginning to the solution of the problem," Emanuel said of Tuesday's moves. "There are systematic challenges that will require sustained reforms. It is a work in progress as we continue to build the confidence and the trust by the public in our police force."

McCarthy was not at the news conference, and did not respond to voice mails or text messages seeking comment.

As late as 8 a.m. Tuesday, he was on the radio talking about the Laquan McDonald shooting and praising the mayor's task force plan.

"How am I? I'm a little busy and a little bit stressed out, but staying the course," McCarthy said when asked how he was doing.

The mayor, however, was changing course after his office issued statements of support for McCarthy during the last week.

For 41/2 years, Emanuel stood by McCarthy through various rocky patches, including a major spike in homicides, and a number of high-profile murders and shootings of young children caught in the gang gunfire of Chicago's most violent neighborhoods.

Then came the intense criticism of how the two handled the police shooting of the 17-year-old McDonald. After Cook County prosecutors charged Officer Jason Van Dyke with first-degree murder a week ago, federal prosecutors disclosed that their probe of the fatal shooting, which was announced in April, remains "active and ongoing."

Van Dyke shot McDonald in October 2014. For much of the last year, Emanuel and his lawyers fought in court to keep a police dash-camera video of the shooting under wraps, arguing that releasing it publicly could interfere with a state's attorney's and federal investigations into the shooting.

But when a Cook County judge's ruling forced Emanuel to release the video to the public last week, the fallout for McCarthy and Emanuel was sharp and immediate. Protesters took the streets chanting "Sixteen shots!" and on Friday blocked entry to Magnificent Mile stores on one of the busiest shopping days of the year.

Black aldermen called for McCarthy to be fired. Cook County Board President Toni Preckwinkle urged Emanuel to do the same. Some Latino aldermen followed suit, as did newspaper editorial writers, television commentators, columnists, and activists nationwide.