New details were released Monday about the tragic shooting death of a 13-year-old girl in Mississippi. A family member tells CBS News the shooting was accidental.

Monroe County officials say a 9-year-old boy shot his 13-year-old sister when she refused to hand over a video game controller.

"He went over to the night stand where there was a gun and he came up behind her and shot her," says Sheriff Cecil Cantrell.

Cantrell says the boy's mother was home when he retrieved the gun which was left unsecured in her bedroom. The boy's aunt said that he thought the gun was fake and unloaded. She adds that he's a straight-A student and the siblings got along well.

"The parents of all families should have their guns and things put in a secure place," said Cantrell.

Twenty two million U.S. children live in homes with a firearm. In nearly half of those homes, the weapons don't have a trigger lock and are easily accessible. While most parents don't think their kids know where they keep their guns, research shows about 75 percent knew just where they were stored, according to the Center for Injury Research and Policy.

Some parents are teaching their kids how to use a firearm CBS News

We recently spoke to parent Paul Risen, who says tragic headlines of deliberate or accidental shootings is why he signed up his 9-year-old son Brody to learn about firearm safety. We saw him learn how to load and fire a .22-caliber handgun during a gun class for kids as young as 8.

"It was fun," Brody says. "It felt good."

Eric and Melissa Keller's sons are 9 and 11. They disagree with the idea that 8, 9 and 10 year olds are too young to learn to fire a handgun.

"We knew a lot about guns by 8 years old," said Eric Keller.

Meanwhile, the sheriff's office says their investigation is still ongoing and right now they have not filed any charges against the 9-year-old boy or his mother.