Use the Porter Outfit to disguise as one of the Train Porter. Since Tesla is not coordinating to solve the mystery, Le Monde suggest that if you dress up like the porter, you can sneak out to Tesla’s room and look for evidence. When you dress up, run to the right until you get to Tesla’s room. Knock on the door and he’ll let you in.
How to Get the Porter Outfit
Once you knew that Tesla was the one who ordered Prune Juice, go to the luggage car, The reporter from Le Monde will be here. She’s standing next to the trunk with the coal smudge on it. The reporter tells you to dress up like the porter, so head to the right and go into the porter’s closet. His outfit is in the room. Use the costumizer to put it on and proceed to Tesla’s Room