The sequence of events that led to the killing of Jason Keys was so confounding that friends and family did not quite believe it until they saw the video evidence played in court.

Mr. Keys and his wife, Charae Williams Keys, were getting into their car after a Father’s Day visit in 2021 with her grandparents in a leafy neighborhood near Walnut Hill Park in Columbus, Ohio. A 72-year-old neighbor carrying a rifle accosted them in the belief, he later told the police, that Mr. Keys had let the air out of his daughter’s tires and poisoned his lawn.

Mr. Keys, who was carrying a pistol in his waistband, and his father-in-law tried to disarm the man, knocking him to the ground, while another relative ran back inside to get a .22 rifle. While Ms. Keys ducked behind the car to call 911, she heard multiple gunshots. She emerged to find her husband mortally wounded.

It took a moment for everyone to realize that the shots had come from a fourth gun across the street. Elias Smith, a 24-year-old ex-Marine, had stepped to his front door with a so-called ghost gun, an AR-style rifle that Mr. Smith had assembled from parts ordered online. Within seconds, he opened fire, hitting Mr. Keys five times.

“What are you shooting for?” a relative of Mr. Keys can be heard asking on surveillance video that captured parts of the incident.

Mr. Smith answered, “I don’t know.”