From the article:
The victim, a 13-year-old girl, was wounded in her upper arm when a boy was showing her his gun and it accidentally went off, a police source said.
The boy, 14, took off after the 6:21 p.m. incident, a police source said. But he turned up nearly two hours later back at the apartment on Elder Ave. near Watson Ave. in Soundview where the shooting occurred, the police source said.
He was taken into custody, the source said.
The article did not say where the boy got the gun.
Every gun in the hands of a child must first pass through the hands of an adult.