Late last month, in the small city of Iguala in southern Mexico, dozens of protesting students were attacked by police and masked gunmen. Six students were killed in the clash, and another 43 remain missing—last seen in the custody of police. Mexican authorities and relatives of the missing now fear that the 43 trainee teachers may have been massacred by local police in league with members of the Guerreros Unidos drug cartel. Yesterday, Mexico ordered the arrest of Iguala Mayor Jose Luis Abarca, his wife, and an aide, charging them with masterminding the attack. Fifty others had already been arrested, including cartel members and dozens of police. A week after the attack, 28 bodies were discovered in a mass grave outside the city, but forensic analysis so far suggests that none of them belonged to the missing students. Hundreds of thousands of Mexicans, enraged by the attacks and the lack of information, have marched in protest across the country, in some places attacking and burning government buildings. Mexican President Enrique Pena Nieto vowed to hunt down those responsible as the government announced a $110,000 reward for information on the missing.