Remember the seventies and the OPEC embargo. Sales of locking gas caps went through the roof!

I had a Honda CB750F that I used to refuel from my girlfriend's father's Plymouth Fury. With the gas cap under the rear plate it was easy to siphon right into the bikes gas tank which I brought right to the car. I broke up with her shortly after he bought a locking gas cap.

Do you know how they got the gas out? If you have a belly tank the route from the fill to the tank is usually to convoluted to get a siphon hose into easily. Did they use the primer ball? If so then they know boats and it would be funny to booby trap some boats with the fuel hose/primer fed into a dummy container of salt water, or used motor oil or something more destructive.