(CNN) Chicago police Officer Jason Van Dyke pleaded not guilty Tuesday to murder and misconduct charges in the shooting of 17-year-old Laquan McDonald .

A few protesters yelled at Van Dyke and called him names as he approached the courthouse for his morning arraignment.

"You just couldn't wait to shoot a black man!" one person shouted.

McDonald was black. Van Dyke is white.

The suspended officer faces six counts of first-degree murder and one count of official misconduct in the killing that was captured on police dashboard camera video . A freelance journalist sued to have the footage released, arguing it was a public record. Mayor Rahm Emanuel said he thought releasing it would jeopardize a federal probe of the case, but a judge found in the reporter's favor and the video became public last month, more than a year after the shooting.

The video shows McDonald walking down the middle of the street. Police later said he held a 4-inch knife in his hand. At least two squad cars are visible, and McDonald can be seen walking away from officers. His back appears to be toward the cars when he is shot 16 times. According to a criminal complaint filed in Cook County Circuit Court, Van Dyke was the only officer to fire his gun among the at least eight other officers who responded. The complaint said that McDonald was on PCP.

Demonstrators were outraged not just about the content of the video, but that it took 13 months to release it

Van Dyke, who remained on desk duty after the shooting, had a history of complaints in his law enforcement career. He was cleared in almost every case. The allegations mostly involve excessive force, and at least one complaint alleges he used a racial slur.

There appear to have been no criminal proceedings against Van Dyke before he was charged in McDonald's death, but a jury did award a Chicago man $350,000 after determining Van Dyke used excessive force during a traffic stop.

Van Dyke's attorney, Daniel Herbert, has said Van Dyke feared for his life and insists that the video doesn't tell the full story. "Video by nature is two-dimensional, and it distorts images," he said. "So what appears to be clear on a video sometimes is not always that clear."

On Tuesday, after Van Dyke's arraignment, Herbert said he is seeking evidence that will clear his client, but he declined to give any details about what that evidence might be.

Criticized mayor takes steps

The uproar over McDonald's killing and last weekend's police shooting and killing of a Chicago grandmother and teenager have inflamed calls for Emanuel to resign, though there is no official process to remove him.

Emanuel's office said this week he planned to cut short a vacation in Cuba and return Tuesday afternoon.

On December 1, in the days after the McDonald video was released, Emanuel announced that he had asked police Superintendent Garry McCarthy to resign, and McCarthy complied.

The mayor then described a new task force on law enforcement accountability that will review how the city trains and oversees its police officers. It will include five Chicagoans who have been leaders in the justice system. Chicago native and former Massachusetts Gov. Deval Patrick will be a senior adviser to the group, Emanuel said.

About a week later, U.S. Attorney General Loretta Lynch said that the Justice Department is investigating whether Chicago police have made a habit of violating the law or the U.S. Constitution in their policing.

"Trust in the Chicago Police Department is broken," Illinois Attorney General Lisa Madigan said in a statement. "Chicago cannot move ahead and rebuild trust between the police and the community without an outside, independent investigation into its police department to improve policing practices."

Van Dyke is the first on-duty officer to be prosecuted for shooting someone since 1968, according to Craig Futterman , a University of Chicago Law School professor and the founder of the Civil Rights and Police Accountability Project at the Mandel Legal Aid Clinic.

Other officers have been prosecuted on charges that they committed crimes while off duty, he noted.

Futterman played a significant role in the release of the McDonald dashboard camera footage.

He was among the first people outside the police department to learn of the video. The professor told CNN that it was a law enforcement official who contacted him.

This person was "shocked, and was afraid that this would be buried," he said. "This person put their career on the line [to speak to me], but I believe their sentiments are represented by a silent majority of officers. The vast majority of officers hate this, what is done by a small percent of officers. These good officers feel disempowered to speak up or do anything about it."

The source described the video frame by frame to Futterman, who then issued a broad statement calling for the video's release. Futterman and journalist Jamie Kalven obtained McDonald's autopsy, which revealed the teen was shot 16 times. That contradicted the official story that McDonald died of one gunshot wound, and seemed to conflict with an account that Van Dyke gave. His partner backed up Van Dyke's account.

In the spring of 2015, major news media begin filing public records requests demanding the video. Around that time, the city paid McDonald's family $5 million. The U.S. Attorney for the Northern District of Illinois and FBI are, meanwhile, investigating Van Dyke, a probe that Emanuel says is the reason the city fought against releasing the dashboard camera video.

In June 2015, represented by Futterman, freelance journalist Brandon Smith filed a Freedom of Information Act request for the video and then sued the police department to compel the video's release. A judge sided with Smith and during Thanksgiving week, the video was published across the country.

Despite the tension in Chicago, Futterman said he feels optimistic about city leadership's opportunity to turn around a police department and restore public trust in law enforcement.

"It feels like a moment that is different than anything I've experienced in my lifetime," he said. "It's the first time that our leaders have acknowledged that there are systemic issues," he said. "The acknowledgment which is the first step toward fixing this."