[Gordon Booth]

I agree with cashman. It's possible someone saw him trying to get in your car, open it then rush off to tell you. Ideal opportunity, in, quick search and away.
It would be awful to accuse him without proof and be wrong and he probably saved you having your insurance go up for the next few years.
No snickering, just bad luck, happens to all of us.

Edit- Just realised Less beat me to it and he's come up with a good idea.