A student wearing a Guy Fawkes mask yells as he stands in front of a banner with white doves, symbolizing the missing Ayotzinapa Teacher Training College Raul Isidro Burgos students, during a protest outside the building of the office of Mexico's Attorney General, in Mexico City November 6, 2014. The students went missing in the town of Iguala in the south-western state of Guerrero on September 26 after clashing with police and masked men, with dozens of police being arrested in connection with a case that has sent shockwaves across Mexico. REUTERS/Tomas Bravo (MEXICO - Tags: CIVIL UNREST CRIME LAW SOCIETY)