BRIDGEWATER, Mass. -- Police are looking for the person who threw a rock off an overpass in Bridgewater and damaged two passing vehicles.

NewsCenter 5's Rhondella Richardson reported that the truck and car were on Route 24 near Walnut Street when they were hit Monday night.

Jeffrey Silva, a police officer, was off-duty and traveling in his friend's car when it was struck by a rock.

"I heard a loud crash on my side of the car in the passenger seat, and the window shattered," Silva said.

Police found a rock on Route 24.

"You could see an actual gouge and some damage," Silva said.

The area of the Walnut overpass is not wide enough to park a car. The rock-throwing incident is a wake-up call to residents and motorists.

"We don't have any idea who is doing it, but we would tell the public in general: Whenever you see suspicious characters hanging around on bridge overpasses, you should call 911 immediately," Massachusetts State Police Sgt. Mike Rafferty said.

A Honda Civic was also hit.

"The passenger's outside mirror -- half of it was ripped right off. There is dirt wedged in the door jam area, so I thought that it must have been a prank. It could have easily resulted in a fatality. It could have gone through the windshield and that could have caused substantial physical injury to either one of us," Silva said.