On the night of Oct. 20, 2014, two officers responding to reports of a break-in at a parking lot came upon Laquan McDonald — black male, six feet, dark hoodie. “This guy, uh, kind of walking away,” one of them radioed calmly at 9:53 p.m. “He has a knife in his hand.” They were eight miles southwest of downtown, on what was little more than an industrial service road, bordered by the Stevenson Expressway and beyond that the valley of a rail yard. The cops treated the situation like the routine encounter that it was. For a quarter mile, they trailed McDonald, one in a squad car and the other on foot, giving the suspect a wide berth so as not to provoke him. Even after the teenager spiked one of the patrol car’s front tires with his three-inch blade, the officers did not fire their guns. Four additional cruisers arrived, three of them hemming in McDonald on his left and one from behind. That’s when Jason Van Dyke emerged from one of these cars and shot McDonald dead.

The cover-up began almost immediately. “He wasn’t dropping the knife, and he was coming at the officer,” a spokesman for the Fraternal Order of Police told the reporters who soon converged on the scene. Describing McDonald as “crazed,” “with a strange gaze about him,” the union representative said that the officer then shot McDonald in the chest: “He leaves them no choice at that point but to defend themselves.” An official department statement was issued hours later: “Officers confronted the armed offender, who refused to comply with orders to drop the knife and continued to approach the officers. As a result of this action, the officer discharged his weapon, striking the offender.”

Craig Futterman, who was a public defender for juveniles on the city’s West Side before starting the University of Chicago civil rights clinic, read the story the following day. “My eyes glazed over,” he said. Like McDonald, a second-generation ward of the state, almost all the people shot by the Chicago police are African-American. A castoff child wandering an urban back of beyond, McDonald seemed destined to be another unremarked addition to the statistics, with little known about the circumstances of his death save what the police reported. Less than three weeks later, however, a whistle-blower from inside law enforcement phoned Futterman. The caller had seen the dashcam video and insisted that it didn’t corroborate the police narrative at all. “That officer shot him like a dog in the street,” Futterman recalls the source telling him. “It was nothing short of an execution.” Futterman says the caller feared that the shooting would be buried like so many others in Chicago. “Please, Craig,” the source implored. “Look into it and let people know.”

Futterman couldn’t go public with news of the video: That would compromise the identity of the caller. But the whistle-blower also told Futterman about a man who had been driving his adult son to the hospital when the police cars swarming around McDonald brought him to a halt. Before he could give a statement to a cop directing traffic, the officer shooed him off with the wave of a flashlight. Jamie Kalven tracked the driver down. He told Kalven that Van Dyke had fired not once or twice to the chest, as the police reports suggested, but until he was out of bullets, at least a dozen times, most of them as the teenager lay helpless on the ground. Van Dyke, the driver told Kalven, had paused to appraise the situation after the first shots whirled McDonald to the ground, and then he continued firing on the prone and lifeless teenager.

That disturbing detail was something that the whistle-blower looking at the soundless dashcam video couldn’t have known. Chicago police cruisers are equipped with cameras and microphones. But a police spokesman told the press in December that more than 80 percent of them don’t record audio because of “operator error or in some cases intentional destruction.” Carol Marin and Don Moseley, of NBC5 in Chicago, found that in the car that captured the video of the shooting, the microphones were in the glove compartment with the batteries installed upside down.

Three weeks after the shooting, McDonald’s mother, Tina Hunter, asked a pair of attorneys, Jeff Neslund and Michael Robbins, to help her look into the circumstances of her son’s death. The lawyers, who would eventually pursue a case, put Kalven in touch with a trucker they found who had been filling out paperwork in a nearby Burger King parking lot when the incident unfolded before him. He told officers that he had just watched what he called “an execution.” According to Kalven and Hunter’s lawyers, the police responded by taking the trucker and two other witnesses distressed by what they’d seen to a station house, interrogating them for hours. Again and again, the increasingly hostile officers responded that video evidence refuted what they claimed to have seen.