Mexico's Federal Attorney General continues to insist that the 43 missing Ayotzinapa students were killed by a drug cartel but that nevertheless the case is not closed. A sharp storm of criticism erupted in response to government declarations on Tuesday that there is no doubt that the students has been killed, with family members fearing that the authorities were trying to prematurely close the case. The government's argument is based on eyewitness testimony and confessions by detained suspects, not physical or scientific evidence. The family members are demanding that other lines of investigation be opened, including on the role of military. Clayton Conn reports from Mexico City.