TUCSON, Ariz. (AP) — A 16-year-old boy has been arrested on suspicion of negligent homicide in the fatal shooting of his younger brother, according to Tucson police.

They said the shooting occurred last Saturday night in an apartment on the city’s south side.

The 13-year-old victim and his older brother were alone in a bedroom when the gun was fired, police said.

Several family members in a different room reportedly heard the shot, and one of the relatives then left the apartment with the 16-year-old before police arrived.

Officers found them a short time later in a nearby church parking lot, and the 16-year-old boy was arrested.

Police said the gun used in the shooting hasn’t been found yet.

They said the 13-year-old boy was declared dead at the scene.

The names of the two brothers haven’t been released by police.