ARLINGTON, Mass — The shell casings found inside an Arlington middle school staircase Wednesday were found to have been dropped by accident, police said Thursday.
The Gibbs School entered a shelter-in-place mode after a staff member found two casings from a 9 mm handgun in the main stairwell around 9:30 a.m.
Police say the casings were traced back to an individual who had attended an event at the school on Tuesday night. Police say the individual has cooperated with police and closed the investigation.
Students were dismissed at 1:20 p.m. due to a previously scheduled early release day.
This is a developing story. Check back for updates as more information becomes available.
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