Keys locked inside 2001 vw beetle?

This just happened to me this morning, well at least I thought it did. I couldn't find the key anywhere, I figured I may have dropped it in the trunk while grabbing the groceries. So I grabbed the universal emergency car key (the wire clothes hanger) and a short flat and wide pry bar. Using a credit card to protect the rear window I created a 1/4 inch gap at the upper corner of the drivers door. We inserted the clothes hanger and was able to get the hook end behind the door latch. We twisted the hanger until the hook forced its way under the handle and then pulled. It really didn't take long to accomplish and left no visible damage to the door. The trunk mechanism was disabled so we dropped the rear seat to gain access to the trunk. Two hours later we found the key between the mattress and the side rail of our bed..... how did it get there?