Police said Monday a maintenance man found two unexploded chemical bombs and officers found evidence that two other bombs had already exploded.
Police say two people were arrested on suspicion of possession of an explosive device.
They are also accused of criminal mischief after police found a mailbox that had been destroyed.
In a separate incident, police called the bomb squad after someone found a bomb with a fuse near a truck on Monday.
Police said the bomb was live and could have rocked nearby residences and businesses, which were evacuated.
The bomb squad used a robot to disarm it. No arrests were reported in the second incident.