A man stands on top of a tractor as a picture of one of the 43 missing trainee teachers is seen during a protest in Mexico City December 5, 2014. The demonstration, which was held by a civil organization of Mexican farmers known as El Barzon, called for the government to find the missing trainee teachers of the Ayotzinapa Teacher Training College 'Raul Isidro Burgos. The text on the picture reads, "justice." REUTERS/Carlos Jasso (MEXICO - Tags: CRIME LAW CIVIL UNREST EDUCATION)