Seattle police say a 10-year-old boy who was shot on a bus turned out to be the victim of his own gun and the aggressor in an attempted robbery.

Police said Wednesday that investigators determined the boy was trying to rob a 17-year-old who had been surrounded on the bus by a group of boys ages 10, 12, 14 and 15.

They say the 10-year-old boy told the teen to empty his pockets.

When the younger boy reached into his backpack, the teen grabbed him in a bear hug. The .22-caliber pistol went off inside the backpack, wounding the 10-year-old in the arm.

Police say the younger boy will face weapon and robbery charges.