Tens of thousands of people have rallied across Mexico over the disappearance of 43 students and the discovery of a mass grave with dozens of burned bodies. The students, who are from a rural teacher’s college, have been missing for well more than a week after police and unknown gunmen ambushed their buses in the state of Guerrero. Twenty-two police officers have been detained, and the city’s mayor and police chief appear to have fled rather than face questioning. On Wednesday, parents of the victims traveled from Guerrero to join the main march in Mexico City, calling on officials to do more to find their loved ones.