A 15-year-old girl who shot and killed her 16-year-old brother claims to have suffered years of abuse at his hands, including being locked in her room for weeks with nothing but a bucket to use to relieve herself, authorities said.

The girl had been left with her brother and two sisters, aged 11 and 3, while her parents were away at work driving in a truck, police said, noting that they had left Sunday and were supposed to be back on Tuesday, according to an Associated Press report.

At some point on Monday, the brother locked her in her room and then went to go sleep, and the girl talked her younger sister into opening the door. Knowing that her parents kept a gun in the house, she used a knife to remove the air conditioner that was in her parents’ bedroom window, and then climbed into the room while her sister kept watch. She grabbed the gun out of a pink bag and load the weapon, according to police.

She then went back in the house and told her sisters to get in a closet, and then began firing the gun at her brother, who was sleeping in the living room and immediately began screaming for help, police said.

After going into another room to collect herself, the 15-year-old girl returned to find the 3-year-old trying to wake up her dead brother, and she fled with her 11-year-old sister, leaving the 3-year-old behind, police said.

Calling it the “stuff of nightmares,” Columbia County Sheriff Mark Hunter said that it was a difficult situation for authorities to handle. Police eventually caught the girls after one of their friends got a strange phone call from the 11-year-old girl saying that she had run away and needed someone to pick her up.

When the woman arrived at the pickup location, the older girl said something might be wrong with her brother, applying makeup as she spoke and appearing emotionless, according to police.

Not long after, she broke down crying, and told police when they caught up with her that her brother was abusive and had beaten her.

Police arrived at the home, where the 3-year-old said, “he’s dead,” as the body lay near the fireplace under a blanket, authorities said.

The father told police that the 15-year-old girl was locked up when she misbehaved and that she had once been kept locked in her room for 20 straight days, and police found just a blanket and a bucket of urine in the closet, authorities said.

The 15-year-old girl had attempted suicide in the past, but law enforcement was not notified. Both girls are in juvenile detention on murder charges, and the prosecutor is trying to determine whether to try them as adults. The parents, meanwhile, were charged with child neglect and failing to supervise. The 3-year-old was taken into the protective care of child welfare officials.