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Sisters, ages 15 and 11, charged with killing older brother

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(CNN) — What would compel a 15-year-old girl and her 11-year-old sister to allegedly shoot to death their older brother?

If police know the motive, they aren’t saying.

The shooting happened in Columbia County, Florida, and the girls themselves contacted police.

Late Monday, deputies went by to investigate and found the 16-year-old boy’s body on the living room floor.

The children’s parents, Keith and Misty Kornegay, were out of town, and allegedly left the three and an additional 3-year-old daughter unsupervised.

The parents were also arrested and charged with child neglect, the county sheriff’s office said. The toddler is being cared for by a child protection agency.

The case is still under investigation, but authorities believe that the older sister took a handgun from their parents’ bedroom and shot her brother. The 11-year-old allegedly assisted her.

While police have identified the girls, CNN is withholding their names since they are minors and have not been charged as adults.

In 2010, the sheriff’s office visited the home on reports of vandalism and a civil matter, CNN affiliate WJAX reported.

Killings are uncommon in Columbia County, which is located between Jacksonville and Tallahassee, Sheriff Mark Hunter told WJAX. There were no homicides there last year.