An investigation is ongoing into an explosion early Saturday at Harvard Medical School that appears to have been intentional, authorities said.

The explosion occurred just before 3 a.m. Saturday morning Goldenson Building on Longwood Avenue, according to Harvard University police.

This photo provided by the Harvard University Police Department shows a person of interest in an explosion at the Harvard Medical School in Boston, on Saturday, Nov. 1, 2025. (Harvard University Police Department via AP)

A university police officer responded to an early morning fire alarm and witnessed two unidentified people running from the building, police said. After attempting to stop the people, the officer entered the building and discovered the explosion.

The Boston Fire Department determined that the explosion was intentional and officers did not find additional devices in a sweep of the building, police said. No one was injured in the explosion, authorities said.

The explosion took place in a fourth-floor hallway, but did not cause structural damage, the deans of the medical school wrote in a message to the community Sunday. They said all labs and equipment remain intact, and the building will reopen Monday.

Police and the FBI released grainy photos of two people wearing face coverings and what looked like sweatshirts.

The deans said the Harvard Police will have an “increased presence” on the Longwood campus and the investigation into the explosion is ongoing.

With reporting from the Associated Press.