The nightmare haunts Victor Dempsey even in his waking hours, tightening his chest and snatching his breath. It is as if it’s waiting for him, and when he sleeps there’s no escape. The dream first came to him when he was waiting for the verdict in the 2017 criminal trial of the police officer who shot and killed—murdered, Dempsey believes—his unarmed brother, Delrawn Small. The two brothers are running, laughing, across rooftops, like they did as boys in their Brooklyn neighborhood of East New York. Then they come to a gap. Dempsey jumps for the next rooftop. He lands it. But as he looks back, calling his brother’s name, he sees Small fall into the inky darkness, and he jolts awake.

On those nights, Dempsey, 33, leaves his fiancé and his three-year-old son, and stumbles sleepily down the stairs of their home in Queens. He sits at the computer and watches the surveillance footage from an auto shop security camera in East New York of the final moments of his brother’s life. The footage, a minute and 45 seconds long, shows two cars stopped at a red light. One carries Small, driving his girlfriend, their young son, and teenaged stepdaughter home from a July 4 barbecue. The other, Wayne Isaacs, a 38-year-old police officer who had just finished a 4 p.m.-to-midnight shift at the 79th precinct in Bedford-Stuyvesant.

Police later told the media that the two drivers had gotten into a traffic dispute moments before Isaacs fired his gun at Small. The video shows Small exiting his car and walking up to Isaacs’s unmarked vehicle. Within seconds, from inside his car, Isaacs shoots Small three times. (The autopsy showed that one bullet pierced Small’s chest, another his stomach, and a third grazed his head.) Small falls back, gets up, lurches a few steps, and collapses between two parked cars.

“I know that video,” Dempsey told me recently. He has watched it hundreds of times, pausing, rewinding, and studying it frame by frame, so carefully that the images of it loop in his mind long after he has left the glare of his computer screen. “I can look at it without looking at it,” he said. The images also torment him with questions: Why didn’t Isaacs roll up the window? Or drive away? Or brandish his badge instead of his gun? “Why did he feel he had the authority to kill my brother?”

Small was the first of three black men whose death at the hands of police over the course of three days in July 2016 gained media attention. On July 5, Alton Sterling, 37, died after police in Louisiana tackled and shot him outside the convenience store where he was selling CDs. The following day, Philando Castile was shot and killed by police in Minnesota during a traffic stop. The horrific eyewitness videos of both shootings immediately went viral on social media. One social media post of the leaked video of Small’s death has since been viewed more than 70,000 times.