A 12-year-old Louisiana girl has been arrested following the death of her 6-month-old brother.

The girl was arrested on Monday, St. Charles Parish Sheriff Greg Champagne announced on Thursday.

Paramedics arrived at a home on the West Bank of St. Charles Parish on Sunday to find the infant not breathing and could not revive him.

An autopsy determined the death was a homicide. Champagne didn’t say how the boy died or how officials came to believe his sister killed him, but said no weapons were involved.

The girl was arrested on a charge of first-degree murder and is being held in a juvenile detention center. Children younger than 14 generally cannot be tried as adults in Louisiana.

The sheriff is not releasing the name of the victim to avoid identifying his sister, calling it a “horrific and tragic situation.”

The Sheriff’s Office waited three days to release information about the homicide and subsequent arrest because the investigation was still underway, sheriff’s office spokesperson Cpl. James Grimaldi told The Times-Picayune ‘ The New Orleans Advocate.