The massacre was a turning point in Mexican history, and the exact responsibility of the officials involved in it continues to be debated, with many asserting that the Secretary of the Interior, Echeverría, was the one who ordered the troops to shoot at the protesters.

[6] With the 1970 elections ahead, Díaz Ordaz "disqualified" both Corona del Rosal and Martínez Manatou from becoming the PRI presidential candidates: in the former's case, because Díaz Ordaz feared that, in the aftermath of the Tlatelolco massacre, Corona del Rosal would be rejected by the population due to his military background; while in the case of Martínez Manatou, he was seen as too close to the dissident sectors that had been behind the 1968 movement.

In an extraordinary move, during his annual Address to the Congress on 1 September 1969, President Díaz Ordaz assumed the full "personal, ethical, social, judicial, political and historical responsibility" for the government's decisions during the 1968 events.

[10][11] The only opposition candidate in the presidential race was Efraín González Morfín, a former legislator, nominated by the right-wing National Action Party (PAN) Whereas Echeverría had been a hardliner during the Díaz Ordaz administration, and had been known as a discreet bureaucrat during his entire career, upon becoming the Presidential candidate he radically changed his image, adopting a populist rhetoric towards the peasants and the students; this was likely to shake off the accusations that he had been responsible for the Tlatelolco massacre.

[13] The military chiefs, including the Secretary of the Defense Marcelino García Barragán, were outraged by the incident and expressed their indignation to president Díaz Ordaz, stating that the Armed Forces would no longer support Echeverría and demanding that he be replaced as the party's candidate.

Nonetheless, Díaz Ordaz stood by Echeverría, who the next day gave an address in which he praised the Armed Forces.