A suburban Chicago hotel was forced to evacuate thousands of guests clad in animal outfits early Sunday after discovering a chlorine leak in the ninth floor stairwell, according to the Rosemont Public Safety Department. Attendees of the annual Midwest FurFest were escorted out of the building and across the street to another convention center hosting a dog show. At least 19 people became ill and were treated at local hospitals, but authorities allowed guests to return after decontaminating the Hyatt Regency O'Hare. FurFest celebrates anthropomorphic animals from books, tv shows and movies. Investigators believe the leak was premeditated and are treating it as a criminal case.