A 12-year-old girl has been charged with murder under juvenile law for allegedly killing her 9-year-old sister, apparently in a dispute over a hamburger.

A Family Court judge will determine if the girl should be tried as an adult, but no date has been set for that proceeding, said Kathryn Herman, assistant administrator for the St. Louis Family Court (search). A detention hearing is set for Wednesday.

The older girl reported finding her sister lifeless on the floor of their home near downtown Dec. 22.

Medical Examiner Michael Graham said Tuesday that the 9-year-old girl had minor injuries to her neck, but an autopsy did not initially determine the cause of death.

On Feb. 1, a social worker told police the 12-year-old was in a hospital psychiatric unit, suffering visions and nightmares, and had told the staff she strangled her sister during a quarrel over a hamburger, police told the Post-Dispatch.

Graham said those statements and the injuries led him to determine the cause of death was strangulation. "No other condition reasonably explains her death," he said.

Police did not immediately respond to calls seeking additional details Tuesday.

Charges against the 12-year-old were filed Thursday, Herman said. She remained hospitalized but was expected to be moved to a juvenile center. If convicted as a juvenile, the maximum penalty would be confinement until her 21st birthday.