Police say a 7-year-old boy alerted a teacher after finding a loaded gun in his backpack at a Philadelphia elementary school.

It happened during an after-school program at Universal Samuel Daroff Charter School in west Philadelphia around 4 p.m. Thursday. School officials told police the boy was putting a folder in his bag at the end of the day and noticed the gun.

The principal says staff immediately took the backpack and called police.

Lt. John Walker says police are conducting interviews with family and reviewing surveillance video to figure out how the gun got into the bag.

Walker says it was a .38-caliber handgun loaded with five rounds of ammunition. The boy says he had his backpack with him in the classroom the entire day.