Juan Manuel Gonzalez was looking for parking on a sunny, quiet street in Upper Manhattan when the sound of three gunshots startled him.

Mr. Gonzalez abandoned his car at the corner of West 163rd Street and Edgecombe Avenue in the Washington Heights neighborhood and found himself caught up in chaos. He saw a man on a sidewalk with severe wounds to his face, he said. A woman was hovering over him. She started yelling.