Domingo Tapia and Gary Anderson crossed paths for no more than a second, two lives colliding in a moment of grainy surveillance footage.

Mr. Tapia, a 38-year-old Mexican immigrant who worked as a fruit vendor, had met his brother for a few beers on a summer evening in 2017. They had passed the time and said their goodbyes.

He turned back momentarily to retrieve a bag of fruit he had forgotten at the bar, mounted his bike and glided off toward his wife and two sons, through the quiet streets of Bedford-Stuyvesant, Brooklyn. It was 1:30 a.m.