“They took them away alive. We want them back alive,” protesters chanted as they marched.

In Mexico City, Murillo said that Sidronio Casarrubias, a leader of the criminal group Guerreros Unidos captured last week, accused Iguala Mayor José Luis Abarca and his wife, María de los Ángeles Pineda Villa, of giving orders to stop the student demonstrations because of a planned political event that Pineda did not want interrupted.

Mexico analysts have blamed government officials and police of strong ties with criminal organizations in Guerrero state.

“We have issued warrants for the arrest of Iguala Mayor José Luis Abarca, his wife, Mrs. Pineda Villa, and police chief Felipe Flores Velázquez, as probable masterminds of the events that occurred in Iguala on Sept. 26,” Murillo said. Both Abarca and Pineda went into hiding soon after the incident.

On Sept. 26, students from Ayotzinapa Normal School, a rural teachers training center that caters to poor and indigenous people, were protesting government reforms they say will make it harder for those on low incomes to afford an education. Shortly afterward, police officials opened fire on the protesters. Six people were killed, including three students, and 43 more went missing in a bout of violence that has shaken Mexico.

Carlos Pérez, a 20-year-old student from the Ayotzinapa Normal School, told Al Jazeera that students were defending their rights to a free education.

“The rural (Normal) schools have a long history of social struggle … and because of that they have faced a lot of harassment, repression, murder — especially in the state of Guerrero,” Pérez said.

A series of mass graves were discovered near Iguala after the student disappearances. Mexican authorities say the remains do not belong to any of the missing students. But an Argentinian forensics team, brought in to help examine the mass graves, cast doubt on that claim on Thursday, according to local media reports. The Argentinian group said it could not rule out that the remains include some missing students because the Mexican federal government did not follow proper protocol in its initial examination of the grave.

Local residents said they had regularly seen trucks driving in the mountains outside of Iguala over past years. They described the entire area as a graveyard.