1968 killing of anti-government protestors by the Mexican Armed Forces in Mexico City
The Tlatelolco massacre () was a military massacre committed by the Mexican Armed Forces against the students of the National Autonomous University of Mexico (UNAM), the National Polytechnic Institute (IPN), and other universities in Mexico.
The massacre followed a series of large demonstrations called the Mexican Movement of 1968 and is considered part of the Mexican Dirty War, when the U.S.-backed Institutional Revolutionary Party (PRI) government violently repressed political and social opposition. The event occurred ten days before the opening ceremony of the 1968 Summer Olympics, which were carried out normally.
On October 2, 1968 in the Tlatelolco section of Mexico City, the Mexican Armed Forces opened fire on a group of unarmed civilians in the Plaza de las Tres Culturas who were protesting the upcoming Olympics. The Mexican government and media claimed that the Armed Forces had been provoked by protesters shooting at them, but government documents made public since 2000 suggest that snipers had been employed by the government. 
The number of deaths resulting from the event is disputed. According to U.S. national security archives, American analyst Kate Doyle documented the deaths of 44 people; however, estimates of the actual death toll range from 300 to 400, with eyewitnesses reporting hundreds dead. Additionally, the head of the Federal Directorate of Security reported that 1,345 people were arrested.
Background.
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 The year 1968 in Mexico City was a time of expansiveness and the breaking down of barriers: a time for forging alliances among students, workers, and the marginal urban poor and challenging the political regime. It was a time of great hope, seemingly on the verge of transformation. Students were out in the streets, in the plazas, on the buses, forming brigades, "going to the people." There were movement committees at each school and heady experiences of argument, exploration, and democratic practice. There was no central leader. Families were drawn in, whole apartment buildings and neighborhoods. A revolution was happening - not Che's revolution - but a revolution from within the system, nonviolent, driven by euphoria, conviction, and the excitement of experimentation on the ground.
 — "Dissent Magazine"
Mexican President Gustavo Díaz Ordaz struggled to maintain public order during a time of rising social tensions but suppressed movements by labor unions and farmers fighting to improve their lot. His administration suppressed independent labor unions and farmers and heavy-handedly tried to direct the economy. In 1958, under the previous administration of Adolfo López Mateos (when Díaz Ordaz was Minister of the Interior), labor leader Demetrio Vallejo was arrested and peasant activist Rubén Jaramillo was murdered.
Arising from reaction to the government's violent repression of a July 1968 fight between rival "porros" (gangs), the student movement in Mexico City quickly grew to include large segments of the university students who were dissatisfied with the regime of the PRI, most especially at the Autonomous National University of Mexico (UNAM) and the National Polytechnic Institute (IPN) but also at other universities. After a fight by rival student groups in central Mexico City was broken up violently by a large contingent of police, university students formed a National Strike Council (CNH) to organize protests and present demands to the government. Large-scale protests grew in size over the summer as the opening of the Olympic Games in mid October grew nearer, and Minister of the Interior Luis Echeverría needed to keep public order. On October 2, 1968, a large peaceful march arrived at the Plaza of the Three Cultures for the usual speeches. However, the Díaz Ordaz government and troops marched into the plaza and gunmen in surrounding buildings opened fire on the unarmed civilians in what is now known as the Tlatelolco massacre.
Assault and massacre.
On October 2, 1968, around 10,000 university and high school students gathered in the Plaza de las Tres Culturas to protest the government's actions and listen peacefully to speeches. Many men and women not associated with the CNH gathered in the plaza to watch and listen; they included neighbors from the Residential complex, bystanders and children. The students had congregated outside the Chihuahua Building, a three-moduled thirteen-story apartment complex in the Plaza de las Tres Culturas. Among their chants were "¡No queremos olimpiadas, queremos revolución!" ("We don't want Olympics, we want revolution!"). Rally organizers did not try to call off the protest when they noticed an increased military presence in the area.
Two helicopters, one from the police and another from the army, flew over the plaza. Around 5:55 P.M. red flares were shot from the nearby S.R.E. (Mexican Ministry of Foreign Relations) tower. Around 6:15 P.M. another two flares were shot, this time from a helicopter (one was green and another one was red) as 5,000 soldiers, 200 tankettes and trucks surrounded the plaza. Much of what proceeded after the first shots were fired in the plaza remained ill-defined for decades after 1968. Records and information released by American and Mexican government sources since 2000 have enabled researchers to study the events and draw new conclusions.
The question of who fired first remained unresolved years after the massacre. The Mexican government said gunfire from the surrounding apartments prompted the army's attack. But the students said that the helicopters appeared to signal the army to fire into the crowd. Journalist Elena Poniatowska culled interviews from those present and described events in her book "Massacre in Mexico": "Flares suddenly appeared in the sky overhead and everyone automatically looked up. The first shots were heard then. The crowd panicked [and] started running in all directions." Despite CNH efforts to restore order, the crowd on the plaza quickly fell into chaos.
Shortly thereafter, the Olympia Battalion, a secret government branch made for the security of the Olympic Games composed of soldiers, police officers, and federal security agents, were ordered to arrest the leaders of the CNH and advanced into the plaza. The Olympia Battalion members wore white gloves or white handkerchiefs tied to their left hands to distinguish themselves from the civilians and prevent the soldiers from shooting them. Captain Ernesto Morales Soto stated that "immediately upon sighting a flare in the sky, the prearranged signal, we were to seal off the aforementioned two entrances and prevent anyone from entering or leaving."
The ensuing assault into the plaza left dozens dead and many more wounded in its aftermath. The soldiers responded by firing into the nearby buildings and into the crowd, hitting not only the protesters, but also watchers and bystanders. Demonstrators and passersby alike, including students, journalists (one of which was Italian reporter Oriana Fallaci), and children, were hit by bullets, and mounds of bodies soon lay on the ground. Meanwhile, on the Chihuahua building, where the speakers stood, Olympia Battalion members pushed people and ordered them to lie on the ground near the elevator walls. People claim these men were the people who shot first at the soldiers and the crowd.
Video evidence also points out that at least two companies of the Olympia Battalion hid themselves in the nearby apartment buildings and set up a machine gun in an apartment in the Molino del Rey Building, where a sister-in-law of then-Secretary of State Luis Echeverría lived. In addition, many snipers were positioned on the roof of the church of Santiago de Tlatelolco and many people involved, including the ones who fired the first two flares, were present at the nearby convent and the Foreign Relations Tower; there was a machine gun on the 19th floor and a video camera on the 17th floor. Video evidence shows 10 white-gloved men leaving the church and bumping into soldiers, who point their weapons at them. One of the men shows what appears to be an ID and they are let go.
By the next morning, newspapers reported that 20 to 28 people had been killed, hundreds wounded, and hundreds more arrested. "El Día"'s morning headline on October 3, 1968, read: "Criminal Provocation at the Tlatelolco Meeting Causes Terrible Bloodshed." A 2001 investigation revealed documents showing that the snipers were members of the Presidential Guard, who were instructed to fire on the military forces in order to provoke them.
Investigation and aftermath.
In 1977, seven years after the end of his presidency, Gustavo Díaz Ordaz was appointed ambassador to Spain by then-President José López Portillo. His appointment revived the debate over his responsibility regarding the Tlatelolco massacre, to which Díaz Ordaz responded by firmly defending his handling of the incident; in an interview on 13 April 1977, shortly before leaving for Spain, a journalist told the former president that his appointment as ambassador "touched a sore spot", to which an upset Díaz Ordaz replied:
 ;templatestyles src="Template:Blockquote/styles.css" / ;"I'm very proud of having been President of the Republic and having thus served Mexico, but what I'm most proud of, from those six years, is the year 1968, because it allowed me to serve and save the country, whether you all like it or not, with something other than hours of bureaucratic work [...], fortunately, we got through, and if it hadn't been for that, you wouldn't have the chance, little boy, of being here asking questions."
In 1998, President Ernesto Zedillo, on the 30th anniversary of the Tlatelolco massacre, authorized a congressional investigation into the events of October 2. However, the PRI government continued its recalcitrance and did not release official government documents pertaining to the incident. In a 2002 "All Things Considered" radio interview with Kate Doyle, director of the Mexican Documentation Project for the US National Security Archive, she described the PRI government's investigations: "I mean, there have been a number of investigations throughout the years. In fact, former president Miguel de la Madrid was interviewed yesterday in the press, and said that he had asked the military and the interior secretary for documents and for photographs of the demonstrations, and was subjected to tremendous political pressure not to investigate. And when he continued to press, the military and the interior ministry claimed that their files were in disarray and they had nothing."
Enduring questions remained after "La Noche Triste" (the Sad Night) that have taken the Mexican government over 30 years to answer. Eventually in 2001, President Vicente Fox, the president who ended the 70-year reign of the PRI, attempted to resolve the question of who had orchestrated the massacre. President Fox ordered the release of previously classified documents concerning the 1968 massacre. The documents revealed that Elena Poniatowska's synthesis of the events that October night was accurate, as Kate Doyle uncovered, Thousands of students gathered in the square and, as you say, the government version is that the students opened fire. Well, there's been pretty clear evidence now that there was a unit that was called the "Brigada Olímpica", or the Olympic Brigade, that was made up of special forces of the presidential guard, who opened fire from the buildings that surrounded the square, and that that was the thing that provoked the massacre.
President Fox also appointed Ignacio Carrillo Prieto in 2002 to prosecute those responsible for ordering the massacre. In 2006, former President Luis Echeverría was arrested on charges of genocide. However, in March 2009, after a convoluted appeal process, the genocide charges against Echeverria were dismissed. The Mexican newspaper "The News" reported that "a tribunal of three circuit court judges ruled that there was not enough proof to link Echeverria to the violent suppression of hundreds of protesting students on Oct. 2, 1968." Despite the ruling, prosecutor Carrillo Prieto said he would continue his investigation and seek charges against Echeverria before the United Nations International Court of Justice and the Inter-American Human Rights Commission.
United States government records.
In October 2003, the role of the United States government in the massacre was publicized when the National Security Archive at George Washington University published a series of records from the CIA, the Pentagon, the State Department, the FBI and the White House which were released in response to Freedom of Information Act requests.
The documents detail: 
Remembrance.
In 1993, in remembrance of the 25th anniversary of the events, a stele was dedicated with the names of a few of the students and persons who lost their lives during the event. The Supreme Court of Justice of the Nation has a mural commemorating the massacre.
During June 2006, days before the controversial presidential election of 2006, 84-year-old Echeverría was charged with genocide in connection