Criminal Damage

Setting out for work this morning, I noticed that two of the stone slabs that top the wall beside the pavement had been disturbed. They're cemented down, so they can't have been easy to move. Then I realised that only one of the slabs was there - I turned round, and saw that the back window of a white car parked in front of the houses was completely smashed in, with rubble lying in the road.
Then the lady from the house across the way shouted me over, and told me that she'd noticed the damage when she went out to walk her dog at around 7am, and she had called the police.
The slab going through the car window must have made quite a noise, but I hadn't heard anything, and nor had any of the other neighbours.
By the time I came home for lunch, the car was gone, the remaining slab had been straightened up and put back in its place, and the rubble on the road had been swept away.

This is not the sort of thing that usually happens in Hay!

Edited to add:

I've just been helping the police with their enquiries, as a young PC came to the door to ask if I'd seen or heard anything. Sadly, I couldn't be of much help. He went off to knock on other doors.