A shell casing was found on a bus at a school in Marlborough on Tuesday morning.
Troopers were called to Marlborough Elementary School, which is located on School Drive, after a spent bullet casing was located around 9 a.m. Police said the training round was found tucked into a bus seat.
State police cleared the school and the bus. No other items were located at the school and the bus.
The incident is under investigation.
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