WEST MIFFLIN, Pa. (AP) — A 10-year-old boy shot his 6-year-old brother to death Wednesday morning while the two were home alone, police said.

Officers and paramedics arrived at the home in West Mifflin, near Pittsburgh, at about 9:45 a.m. Wednesday to find Julian Hoffman with a gunshot wound to the head, authorities said. He was taken to a hospital, where he later died.

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Investigators determined the 10-year-old fired the gun in their mother’s bedroom.

The mother, who was not identified, was at work when the shooting happened, said Superintendent Coleman McDonough. After the boy was shot, the 10-year-old first called his mom and then called 911 at her urging, he said.

The investigation was ongoing and no charges were filed as of Wednesday afternoon.

The boys lived at the home with their mother and her boyfriend. The gun, a 9 mm pistol, appeared to be legally owned by the woman, McDonough said, but he wouldn’t comment on how the gun had been stored.

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“There’s really no excuse for a weapon to get in hands of a child,” he said.

Neighbor David Meir told TV news stations he heard loud noises and screams Wednesday morning but wasn’t alarmed until he saw police later in the day. He said he often saw the boys playing outside.

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