The Silly Season

Lawmommy at (where else?) Law and Mommyhood pointed me toward this story, about a mysterious rain of money in Aberystwyth, Wales. And it's a perfect little 'silly season' story:

"Someone around the corner said he saw a man get out of a car, go to the pedestrian crossing and throw a huge bundle of money into the air," according to a shopkeeper.

But what caught my attention was this bit of information:

Police ... stressed that most of the money had been recovered.

On what grounds did the police "recover" the money? How come the people who picked it up didn't get to keep it? Is there some law in Wales about taking money from an eccentric stranger?