The hotel room

While cleaning out the attic of your deceased great-grandfather Carl, you found a suitcase containing a postcard, a newspaper clipping, and a photo. The postcard was sent to Carl in October 1910 and mentions Isabelle who had left something behind in room 13 at Hotel Antoinette - something that appears to be valuable. A few days later, the newspaper reports that the hotel owner has gone mad and murdered all the hotel guests - the hotel closes down and is now said to be haunted. Of course, you are not afraid of any ghosts and are terribly curious about whether the object might still be in room 13, so you head over there...