MERCER, Pa. — A 7-year-old boy had been buckling himself into his safety seat in the back of his father’s truck when he was shot to death after a handgun accidentally went off as his father got in the front seat, police said Sunday.

Joseph V. Loughrey, 44, told police he had been trying to sell the guns Saturday at Twigs Reloading Den in East Lackawannock Township, 60 miles north of Pittsburgh. He unloaded the magazine at home, but didn’t realize a bullet was still in the chamber, Lieutenant Eric Hermick said. His son, Craig Allen Loughrey, was shot in the chest and died at the scene.