Two people are in custody after breaking through the gates to Moon Island in Quincy on a stolen moped Monday, police said.
Quincy police didn't immediately have more information about what took place.
The island is owned by the city of Boston and hosts a firing range for its police department and the training academy for its fire department.
Aerial footage showed a scooter on the island's causeway and someone in custody near the entrance to a building.
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This developing story will be updated when more information is available.