about those fingerprints-- i've thought about this.. so get ready...
There are a lot of those stories- about how ghosts will push your car uphill and you can see fingerprints in talcum powder, etc. They can be civil war casualities or children on a RR track, but they're everywhere. When you sprinkle the powder on the bumber, move the car a little bit, get out and look at it there are fingerprints. Now, where you sprinkle the powder is usually near the end on the door for the trunk, no? When people close their trunks, they usually place their hands on the edge, and throw it downward. And if i remember correctly, in the afformentioned TV show, that is where most of the fingerprints were- on the trunk. Now unless you've just recently scrubbed your trunk door thoroughly, there is going to be a lot of oils and prints from your hand closing the trunk. The oils will no doubt grab whatever powder is thrown at it.