PARIS, FRANCE - NOVEMBER 15:  A French flag flies at half mast on the roof of the Louvre musem on November 15, 2015 in Paris, France. As France observes three days of national mourning members of the public continue to pay tribute to the victims of Friday's deadly attacks. A special service for the families of the victims and survivors is to be held at Paris's Notre Dame Cathedral later on Sunday.  (Photo by David Ramos/Getty Images)