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People march to mark the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Marco Ugarte) ( Mexico Massacre Anniversary )

A student with his mouth covered with the word "Justice" carries flowers during a protest marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

People demonstrate on the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A masked protester spray paints a wall during a march commemorating the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968, days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

Masked protesters run during a march commemorating the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

Police put out a fire during clashes that broke out during a march commemorating the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

Masked protesters clash with riot police during a march marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers ten days before the 1968 Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A police officer is engulfed in flames after being hit by a Molotov cocktail thrown by protesters marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers ten days before the 1968 Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A protestor throws a stone during clashes with police at a march commemorating the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A police officer yells at photographers to stop taking pictures of clashes with demonstrators who are marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968, days before the Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( APTOPIX Mexico Massacre Anniversary )

Protesters and police clash during a march marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Marco Ugarte) ( Mexico Massacre Anniversary )

Protesters attack a police officer during a march marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers in 1968 days before the Summer Olympics celebrations in Mexico City. (AP Photo/Marco Ugarte) ( APTOPIX Mexico Massacre Anniversary )

A police officer's shield is covered in red paint that was thrown by protesters marking the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest, killed by men with guns and soldiers ten days before the 1968 Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A man on the ground holding a microphone who yelled that he is a journalist is kicked by police during a march by protesters on the anniversary of the Tlatelolco massacre in Mexico City, Wednesday, Oct. 2, 2013. The officers left the scene after other members of the media intervened on the man's behalf. Mexico commemorated the 45th anniversary of the massacre of students holding an anti-government protest days before the 1968 Summer Olympics celebrations in Mexico City. (AP Photo/Eduardo Verdugo) ( Mexico Massacre Anniversary )

A group of young men rioting in the Plaza of the Three Cultures district of Mexico City in Mexico City on Oct. 3, 1968. (AP Photo) ( Mexico City Riots )

Mexican army soldiers crouch with weapons ready in Mexico City's Tlatelolco district, in this October 2, 1968 photo. The truth behind the stunning assault on a peaceful democracy protest known as the Tlatelolco Massacre in which some 300 people are believed to have been killed remains largely hidden by government and military secrecy. (AP Photo/STR) ( MEXICO MASSACRE )

These are among 125 Mexican students who were taken into custody in Vocational School No. 7 in Mexico City's Tlatelolco district just north of the main downtown section, Oct. 3, 1968. The school was a focal spot of the newest outbreak of violence last night which cost at least 25 their lives. (AP Photo/William A. Smith) ( Tlatelolco Massacre )

University students, right, in underwear are hold at gunpoint by soldiers inside an apartment building in Tlatelolco, Mexico City, in this Oct. 2, 1968 photo. A Mexican magazine published photos, including the one shown, showing that paramilitary forces hired to provide security during the 1968 Olympic games apparently participated in a massacre of student protesters _ something past Mexican governments have denied. (AP Photo/Proceso) ( MEXICO MASSACRE PICTURES )

University student Florencio Lopez Osuna, badly beaten, poses for an unknown photographer inside an apartment building in Tlatelolco, Mexico City, in this Oct. 2, 1968 photo. A Mexican magazine published photos, including the one shown, showing that paramilitary forces hired to provide security during the 1968 Olympic games apparently participated in a massacre of student protesters _ something past Mexican governments have denied. (AP Photo/Proceso) ( MEXICO MASSACRE PICTURES )

Two burned-out buses testify to the violence of riots in Mexico City where a score or more persons were killed and many others wounded in the worst outbreak of student disorders since they began several months ago, Oct. 3, 1968. (AP Photo) ( Tlatelolco Massacre )

Mexican troops stands by their machine guns in front of the Chihuahua building on the Plaza of the Three Cultures in Mexico City, Oct. 3, 1968. This was the scene of last night's bloody battle between soldiers, police and students. (AP Photo) ( Tlatelolco Massacre )

Student sympathizers lay floral offerings for the 35 persons who died in a student-government riot one month ago, outside a church in the Plaza of the Three Cultures near downtown Mexico City, Nov. 2, 1968, Day of the Dead. There were no incidents. (AP Photo/Joe Caneva) ( Tlatelolco Massacre )

Cesar Perello, a spokesman for the Mexico University students, gives a pledge of no more violence at a press conference in the auditorium of the University’s Medical Center in Mexico City, Oct. 5, 1968. With him are other leaders of the students’ “strike committee”, Cesar Tirado, left, Roberto Escudero (with glasses) and Jose Nassar, right. (AP Photo) ( Tlatelolco Massacre )

Youngster with a bottle in each pocket, at the site where an estimated 10,000 striking students held a meeting at the Santo Tomas section of the Polytechnic Institute, in northwest of Mexico City, Nov. 19, 1968. It was the first time the students gathered without incidents since their bloody confrontation with authorities early last month. (AP Photo/Jesus Diaz) ( Tlatelolco Massacre )