26-year-old Galen Hawk, of Ninepipes, Montana, was playing with his 3-year-old nephew, Lonato Moran-Allen.
According to documents, Hawk saw the boy holding his handgun and he took it away from him. Hawk said the boy then ran down the hallway, looking back toward him while pretending to shoot a toy gun. Hawk responded by pointing his gun at Lonato and pulled the trigger.
The gun discharged, shooting the boy in the back. The boy died at the scene.
Hawk said he thought the gun wasn't loaded because he had the magazine for the gun in his pocket. He also told investigators that before the shooting he had been drinking whisky and alcoholic lemonade.
Hawk was charged with negligent homicide. He faces up to 20 years in prison.