Demonstrators march to protest the disappearance of 43 students from the Isidro Burgos rural teachers college, in Mexico City, on October 22, 2014. Tens of thousands marched in Mexico City's main avenue demanding the return of the missing students. The Mexican government says it still does not know what happened to the young people after they were rounded up by local police in Iguala, a town in southern Mexico, and allegedly handed over to gunmen from a drug cartel on September 26, even though authorities have arrested 50 people allegedly involved, including police officers and alleged members of the Guerreros Unidos cartel. #

Students from Ayotzinapa Teacher Training College Raul Isidro Burgos hold pictures of missing students outside the Attorney General building in Chilpancingo, in Guerrero, on October 7, 2014. #

A teacher who did not want to be identified lies in a hospital bed on September 30, 2014, recovering from two bullet wounds suffered during the previous weekend's clashes with alleged state police in Iguala, Guerrero state, Mexico. Fourteen of 57 students who vanished after deadly shootings in southern Mexico turned up alive but relatives feared for those still missing as authorities search for them. #

Mexican marines and officers belonging to the Attorney General's Office guard an area where clandestine mass graves were found near the town of La Joya, on the outskirts of Iguala, Mexico, on October 9, 2014. Two weeks after 43 students disappeared in a confrontation with police in rural southern Mexico, Attorney General Jesus Murillo Karam announced that suspects had led investigators to four new mass graves near the southern city of Iguala where authorities unearthed 28 badly burned bodies a week earlier. #

Clandestine graves near Iguala, Mexico, on October 6, 2014. Despite efforts to identify the 28 bodies found in these graves, they remain unidentified, forensic evidence so far ruling out the possibility that they were the missing students who were attacked by local police in Iguala. #

Protesters march during a demonstration in Mexico City on October 8, 2014, demanding justice in the case of the 43 students that went missing in Iguala on September 26, after a clash with local police. Thousands of people protested around the country on Wednesday amid fears the students were executed by a gang working with crooked police. #

Students from the Ayotzinapa Teacher Training College throw stones at the windows of the City Congress in Chilpancingo, in the Mexican state of Guerrero, on September 29, 2014. Students from the college demonstrated in the streets to demand the safe return of students who remained missing after a series of clashes. #

A police helicopter flies overhead as the Guerrero state capital building burns after it was set on fire by protesting college students in Chilpancingo, Mexico, on October 13, 2014. Hundreds of protesting teachers and students demanding answers about the 43 students who went missing on September 26 during a confrontation with police, clashed with police at the local congress and outside the state government palace. #

Furniture burns after protesters attacked the municipal palace in Iguala, Mexico, on October 22, 2014. Hundreds of protesters destroyed and set fire to the municipal palace of the town. #

Mexican federal police and Attorney General's officers take part in a security operation in the Ejido de Carrizalillo, Guerrero State, Mexico, on October 21, 2014. Mexico's government announced a $110,000 reward for information on the disappearance of 43 students in a case of alleged collusion between a drug gang and police. #

A member of the Mexican Gendarmerie, with a dog on the outskirts of Cocula, Guerrero State, Mexico, on October 19, 2014, searching for students who went missing in Iguala on September 26. #

Municipal police officers who are suspected of being involved in the disappearance of 43 students are marched to waiting transport at the Mexican attorney generals' organized crime unit headquarters in Mexico City on October 17, 2014. #

Photos of missing students are displayed during a march in support of the Ayotzinapa Teacher Training College missing students, in Mexico City, on October 8, 2014. Thousands marched through the Mexican capital on Wednesday to demand the government find out what happened to dozens of missing students, who are feared to have been massacred by gang members and police. #

Theater students take part during a protest in support of missing Ayotzinapa Teacher Training College students, outside the building of the office of Mexico's Attorney General in Mexico City, on October 15, 2014. #

Supporters of the Zapatista National Liberation Army (EZLN) stand during a protest in support of the 43 disappeared Mexican rural college students, at a main road near San Cristobal de las Casas, Mexico, on October 22, 2014. #

Demonstrators protest the disappearance of 43 students from the Isidro Burgos rural teachers college in Acapulco, Mexico, on October 17, 2014. Thousands of protesters marched along Acapulco's famed coastal boulevard demanding the safe return of 43 missing students from a rural teachers college. #

A woman holds a photograph of a missing student during a march in support of the Ayotzinapa Teacher Training College missing students, in Monterrey on October 8, 2014. #

People attend a protest against the disappearance of 43 students from the Isidro Burgos rural teachers college, at the Zocalo, Mexico City's main square, on October 22, 2014. Tens of thousands marched in Mexico City's main avenue demanding the return of the missing students. #

A burning overturned car stands between protesting students and riot police after it was set on fire by protesting college students outside of the Guerrero state capital building in Chilpancingo, Mexico, on October 13, 2014. #

An activist throws a chair towards a window inside the Municipal Palace during a demonstration to demand information about the 43 missing students of the Ayotzinapa teachers' training college, in Iguala, Mexico, on October 22, 2014. #

A firefighter stands next to graffiti reading "Narcogovernors traitors", while putting out a fire after teachers and students set the Democratic Revolution Party (PRD) headquarters ablaze in Chilpancingo, Guerrero state, on October 21, 2014. #

A journalist takes a picture of a car, overturned by what security officials say were protesters with the Ayotzinapa Teacher Training College in Chilpancingo, in the driveway of Guerrero Governor Angel Aguirre's residence in Guerrero, on October 4, 2014. #

Women march during a protest against the disappearance of 43 students from the Isidro Burgos rural teachers college, in Mexico City, on October 22, 2014. Tens of thousands marched in Mexico City's main avenue demanding the return of the missing students. #