A mistrial has been declared in the case of a police officer in Washington state who was charged with manslaughter after his 3-year-old son shot and killed one of the officer's other children after finding a gun in the family van.

Derek Carlile is accused of leaving a loaded .38-caliber revolver in a cubbyhole in the van, then getting out and leaving his four young children inside. Investigators say the 3-year-old grabbed the gun and fatally shot his 7-year-old sister.

On Tuesday, the jury was declared hung.

Prosecutor Lisa Paul says, "No reasonable person would leave a loaded, unsecured gun in a van with four children."

Defense lawyer David Allen told the jury that the shooting was a tragic mistake.

Carlile will be retried in January.