A bullet shell was found in Wellesley High School's locker room after school Monday afternoon, leading to a search of all the athletic lockers and students' backpacks, police said.
The shell was for a .22-caliber gun, though it was a "dud round," meaning it was not actually capable of being fired from a gun, said Wellesley Police Lt. Marie Cleary.
The shell was found on the floor around 2:45 p.m. as the locker room was being cleaned, Cleary said. All the athletic lockers were searched, as were the backpacks of students who were still on campus after school for activities, she said.
"Everyone cooperated with the search," she said.
Cleary said that police are working with school officials to investigate the incident.
"To find any type of expended round or round of ammunition in a school is unusual," she said. "We'll be working with the school to ensure the safety of all students and staff at the school."
Wellesley superintendent David Lussier said that a message was sent to parents about the incident.
"This bullet was not a live round - it was already spent," he said. "At some point it could have fallen out of someone's pocket."
Lussier said the school saw it as an isolated incident, and noted that whomever was responsible would face discipline from the school and police if caught.
"Bringing a round into school is very serious," he said.
Jaclyn Reiss can be reached at firstname.lastname@example.org