Lives were put at risk after slabs of cement were thrown from a road bridge in County Down, police have said.
Police said the lives of motorists had been put at risk
Three drivers escaped injury after the slabs were thrown from the bridge at about 1900 GMT on Monday.
The objects were thrown from the Cascum Road bridge on the A1, just outside Banbridge. Two lorries and a coach were damaged in the incident.
Coach driver Norman Ingram said: "It was very frightening - it was lucky there were no passengers at the time."
"I was driving under the bridge when I saw the concrete block coming down," he said.
"I didn't see anyone beforehand - it was dark at the time and I had my lights on.
Norman Ingram said the incident was frightening
"It banged right into the front of my cab, smashing lights and damaging the paints. It caused damage worth at least a couple of hundred pounds."
Mr Ingram said the block which struck his coach may have come from a nearby building site.
"I reckon it wasn't small kids who did this because the block was tossed over to hit the windscreen, and small kids wouldn't be able to get it on target - a bit of organisation went into it," he said.
Police have appealed for anyone with information to contact them.
They said they would "deal robustly" with those responsible.