Police said the boy discovered the gun about 4 p.m. Thursday, the Philadelphia Daily News reported. The third-grader was at the Samuel Daroff Charter School in West Philadelphia and was getting ready to go to an after-school program.
The boy told his teacher about the gun and police were called to the school. A SWAT team removed the weapon, a .38-caliber revolver, from the backpack after police discovered there was a problem with the barrel.
Detective Lt. John Walker said the boy's mother and uncle were questioned, The Philadelphia Inquirer reported. Walker said it was unlikely someone at school stashed the weapon in the backpack, although that was a possibility.
"The kid did the right thing," Walker said. "The school did the right thing. Now we're going to find out who did the wrong thing."
This was the third incident since Jan. 1 involving a gun at a Philadelphia school. On Jan. 11, a woman who allegedly tried to take a gun into the building in a diaper bag was arrested at South Philadelphia High School and a ninth-grade student was apprehended allegedly smuggling a gun into Benjamin Franklin High in his shoe.