The Associated Press reports that four students have been arrested in San Francisco after a gun was discharged on school grounds. Police recovered a gun and spent bullet casing on the grounds of Balboa High School.

One student was determined responsible for the discharge of the gun, and the other three are suspected to be accessories after the fact.

Because the four suspects are underage, their names haven’t been released.

One student was treated for a minor injury that wasn’t related to the gunshot.

Authorities were called at 11:15 a.m. on Thursday and it was surrounded with officers with guns drawn. The school was on lockdown as well as three others in the area.

*Photo credit Karl Mondon/Digital First Media/East Bay Times/Getty Images