SAN BERNARDINO, Calif. — Authorities in Southern California say a woman has been arrested after her 12-year-old son accidentally shot and killed his twin brother.

San Bernardino police say they responded to a shooting around 7:30 p.m. Monday and found the boy, who died at a hospital.

The department says an investigation revealed the siblings got hold of an unlocked handgun while they were home alone and loaded it.

Police say the boys were playing with the gun when it accidentally went off.

Their mother, 45-year-old Gabriela Keeton, was arrested Tuesday on suspicion of felony child endangerment. She was being held on $100,000 bail. It wasn’t immediately clear whether she had a lawyer.

Authorities tell KABC-TV that the boys’ father was in the hospital at the time but didn’t provide details.