The Chicago Police Department, on November 24, released a dashcam video taken over a year earlier of Police Officer Jason Van Dyke fatally shooting 17-year old Laquan McDonald.

In the weeks following the shooting, University of Chicago Law School professor Craig Futterman and reporter Jamie Kalven of the Invisible Institute, a South Side nonprofit, received confidential tips from law enforcement about the video’s existence. The release of the video was made possible by the attention Futterman and Kalven brought to the case, in the media and the courts.

According to the Cook County State Attorney’s Office, the United States Attorney’s Office, and the FBI, McDonald had broken into trucks prior to the incident. Upon learning this, police dispatchers asked if any available units had Tasers. Officer Van Dyke’s unit responded to this call without specifying whether it did.

The video shows McDonald walking away from Officer Van Dyke with a 3-inch knife. The officer takes a step towards McDonald and fires sixteen shots from ten feet away, in the span of fourteen seconds – during thirteen of which McDonald was on the ground, according to official analysis. Of the eight officers present, only Van Dyke fired his weapon. Toxicology reports showed that McDonald had traces of PCP in his system. He died in transit to Mt. Sinai Hospital.

The City paid a 5 million dollar settlement to McDonald’s family in April, months before the video was released.

After obtaining witness accounts and autopsy reports, Futterman and Kalven made a public request in a December 2014 article on the Invisible Institute’s website that the city release the video. There was no response.

The autopsy report allowed their case to gain traction, revealing the number of shots fired by Officer Van Dyke to be sixteen–before listed only as “multiple” in police accounts. “The next big break in the case was a tip from sources about the contents of the autopsy report. In February I published a piece in Slate magazine that detailed what I knew about the autopsy, which was radically at odds with the initial report of the police. I saw what they’re chanting about in the streets now, the sixteen shots,” Kalven said.

Several weeks after the release of the autopsy report in February, local and national news sources filed Freedom of Information Act (FOIA) requests for the video – all of which were denied. But during probate, the process by which one’s estate is divided after death, McDonald’s lawyers were able to issue a subpoena for the video.

Following this subpoena, the police continued to delay the video’s release until two weeks ago. “The CPD’s primary arguments against the release of the video were that it would compromise the integrity of its ongoing investigation. But the court found that the CPD was not conducting any part of the investigation, and moreover that the release of the video would not jeopardize any investigation into the shooting,” Futterman said.

Protesters against police brutality have responded strongly to the video, and its release led Mayor Rahm Emanuel to ask for the resignation of CPD Superintendent Garry McCarthy. The head of Chicago’s Independent Police Review Authority resigned on Sunday, and the CPD’s Chief of Detectives announced his retirement on Monday. The same day, Attorney General Loretta E. Lynch announced that the Justice Department will investigate the CPD.

“It’s ironic about where we are today that this terrible, tragic, utterly wasteful event is now an incredibly valuable public resource. This story of the police department and the city at every turn circling the wagons – putting forward a narrative they knew was false, maintaining that false account by destroying evidence, intimidating witnesses, and falsifying police records, as I’m sure will be revealed in the coming weeks – can now be used as a weapon to rally people for reform,” Kalven said.

He added that Chicago, as well as the rest of the country, is at the threshold of police reform, though it will only come  incrementally. “I think change will come, and I’m optimistic, but it’s going to require all of us. We’ve got a lot of work ahead.”