A boy of 10 accused of shooting dead his mother may have argued with her about carrying firewood into the house.
Deborah McVay, 46, was found dead in her living room from a single gunshot wound to the head on Sunday in Big Prairie, Ohio.
Joseph McVay may have argued with her over household chores, sheriff's deputy Nathan Fritz said on Tuesday.
He said: "There may have been an argument over whether he should bring firewood into the house and possibly it escalated from there."
Four weapons were found in the boy's bedroom. On his bed were the .22 calibre rifle believed to have killed his mother and a 12-gauge shotgun. On a gun rack mounted to the wall hung two more .22 rifles. Police were called to the house, in rolling farmland, after a neighbour called to say the boy had come to her home and said he had just shot his mother.
"I'm her neighbour. I'm over here. She's bleeding from her head," the neighbour told an operator. When she was asked "Is she breathing?" the neighbour answered, "no, she's bleeding."
"The neighbours came over and got me and said the mom got shot in the head," the neighbour said.
Family members have told authorities that the guns were a present from the boy's late grandfather. "It's not unusual for boys of that age to hunt and shoot," said Mr Fritz. "I think it's unusual that those weapons were permitted to be in the boy's bedroom."
The boy lived with his mother and 15-year-old sister - who was present at the time of the shooting - in the small one-storey dwelling. Several relatives live nearby, including Deborah McVay's mother.
The investigation has unearthed previous disciplinary problems in the 10-year-old's life, but no serious violence. In September 2007, the boy was disciplined for hitting his elementary school principal in the face and chest with a dustpan. The principal had been escorting the boy to the gym for a "time-out" after he had been disruptive in class.