According to the Dutch news last night, the couple asked someone on the street if it was OK to camp nearby as it was very late in the evening and they could not find a camping. The man showed them a place behind a house and said it was OK to camp there.
Late at night they came back. http://wtop.com/index.php?nid=105&sid=1465228
The husband identified the man who did this and they have been caught.