BOSTON (AP) — A Harvard Medical School building has reopened while a “very active” investigation continues into a weekend explosion that authorities said was intentionally set off.

An officer who responded to a fire alarm early Saturday morning encountered two people running from the Goldenson Building, according to university police. The explosion occurred on the fourth floor of the building, which houses labs and offices associated with the medical school’s Department of Neurobiology.

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.

“The small section of the fourth-floor hallway where the explosion took place has been cleared and is fully operational. There

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