At our recycling yard, maybe 3 years ago, I noticed that the used cooking oil containers were empty. We need a form from the pick up company, so we know how many liters they take, and we can figure out what they owe the county. So I called up the ladies in the office and asked them to call the pick up company. She called me later, and said the pickup company had not been to my site, and they were not about to write a form and pay the county for what they had not picked up. No one could figure who would steal 200 liters of used cooking oil.
A half year later, same deal. And not just at my site. Then one day a guy at a site right down the road, noticed a VW Passat, come in, and it smoked bad, and smelled for all the world like french fries. He took a picture of the license plate, the guys face and called it a day. Two days later, all the cooking oil was gone. Didn't take John Law very long to crack that case. But, here is the sad joke. The judge did not allow the pictures as evidence, as its against the law to take a pictures of someones face, without getting permission. They still busted him for running an unauthorized fuel.