Here's the guy.
I called Fairfax Police. I got the number from 411 and asked for the non-emergency Fairfax Police phone number. The dispatcher asked for my name, phone number, location and a description of the car. She thanked me and was SUPER nice. It took less than 2 minutes to report the guy. (I later found out that 411 connected me to the emergency dispatch line... but that didn't seem to matter.)
We rode back past an hour later and VOILA! The car had been moved!
It is now MUCH safer to ride, walk and ski on the trail. Thank you Fairfax County Police! You have proved yourself AWESOME again!
When you see something like this, please take a few moments to take action. You'll make the world a better place... even if it is just a small corner of the world.