A 15-year-old boy was arrested Monday on charges that he shoved a gun under a seated Muni passenger while trying to hide the firearm from police.
Around 7 p.m., police said, officers stopped a southbound bus at San Bruno Avenue and Dwight Street on a report that a passenger was armed.
The suspect watched the officers "cautiously" through the bus window as they approached, police said. When they boarded the bus, the teen "lunged at a passenger seated beside him and shoved an item underneath him."
That bystander immediately stood up, police said, revealing the loaded .357 caliber pistol.
The 15-year-old, whose name is not being released because he is a minor, was arrested and booked at the Juvenile Justice Center on weapons charges.
Police are now investigating whether the gun had been used in previous crimes.