Tens of thousands marched in Mexico City on Thursday, demanding that authorities find 43 missing college students. Officials had canceled the traditional Nov. 20 Revolution Day parade, and marchers carrying “mourning” flags with Mexico's red and green national colors substituted by black suggested the country was in no mood for celebration. Protesters converged on the city’s main square, where families of the missing students stood on a platform in front of the National Palace holding posters of their relatives’ faces. Amid chants for President Enrique Peña Nieto to step down, family members repeated that they do not believe the government’s account that the youths were killed by a drug gang. The largely peaceful demonstration turned violent at the end, as a small group of masked protesters battled police in the main square.