Ben Franklin High School went on lockdown Wednesday afternoon after a single shot was fired and a bullet casing was found on campus. Now three people are in police custody, ABC Philly reported.

The identities of the three individuals have not been revealed by investigators, and there are no reported injuries.

"Police say that it began with a fight involving a group of students in a stairwell, when one student fired a gun, ABC Philly reported. "The other students fled the area and reported the incident. When officials investigated, they found a spent shell casing and placed the school on lockdown."

There is no word yet on whether a gun has been recovered by investigators.

Matt Lee is a web producer for Metro New York. He writes about almost everything and anything. Talk to him (or yell at him) on Twitter so he doesn’t feel lonely @mattlee2669.