A relative of the 43 missing students of Ayotzinapa Teacher Training College Raul Isidro Burgos holds a poster in a news conference in Mexico City October 29, 2014. Mexican authorities on Monday said they had arrested four drug gang members involved in the kidnapping of the dozens of student teachers who disappeared last month and are feared massacred. Forty-three students disappeared in Iguala on September 26 after they clashed with police and masked men. [Photo/Agencies]