SAN FRANCISCO (AP) — Police said they arrested four San Francisco students Thursday in connection with a gunshot on a high school campus that injured no one but prompted a lockdown and canceled classes.

A gun and spent bullet casing was recovered on grounds of Balboa High School, San Francisco police spokeswoman Grace Gatapandan said.

She said one of the students is responsible for the gun and it discharged. The other three were arrested on suspicion of being accessories after the fact.

Police don't release the names of suspects younger than 18.

One student suffered a minor injury unrelated to the gunshot and was treated and released to their parents.

Officers were called to the school in the blue-collar Excelsior neighborhood on the city's south side around 11:15 a.m., and officers surrounded the campus with guns drawn.

The school was locked down and three others in the area went on lockdown as a precaution.

A news station's helicopter later captured video footage of police escorting a young male in handcuffs from the school to a patrol car.