U.S. national flags fly at half mast at the Washington Monument to mourn the victims of a mass shooting at a concert in Las Vegas, in Washington D.C., the United States, on Oct. 2, 2017. At least 59 people were killed and an estimated 515 people transported to hospitals in a mass shooting at a concert in Las Vegas in the U.S. state of Nevada, police said on Monday. (Xinhua/Yin Bogu)