Use the Luggage Key to open the trunk with coal handprint. You’ll find the invention of Edison Thomas here! And then Le Monde reporter leaves to go get the security guards. At first, it looks like the owner of the truck is Tesla, but later on the investigation the real owner was the Le Monde reporter.
How to Get the Luggage Key
You will need to wear Porter’s Outfit to get in to Tesla’s cabin, he’ll ask for a refill of prune juice. Grab the pitcher sitting on the dresser to the left and then keep refilling his glass. Soon, he’ll need to use the bathroom. This gives you a chance to search for clues in his room while he’s gone. Click on random objects in the room. You can see Tesla leaving and going to the bathroom in a picture-in-picture window above. I tried clicking everywhere and I think the game is rigged so that you always find the key at the last possible moment: just keep clicking around. Anyway, you’ll get the Luggage Key.