THE BAG THEY MISSED

The police received a report about six thieves who stopped a van which carried factory wages.
After three hours the policemen found the van near the river. The driver said the thieves had obliged him to drive up to the river, had tied him up and gagged him with a handkerchief so that he couldn't shout. Then they had thrown him into the back of the van. There was two bags in the back and the thieves had stolen only one.
Afterwards, a policeman asked him how much money there was in the bag. The driver laughed and explained that there wasn't any money in the bag the thieves had stolen and that the wages were in the bag he had been sitting on for three hours!