Article published on the 2008-10-03 Latest update 2008-10-03 15:23 TU
Thirty thousand people had gathered in the Mexican capital to mark the 40th anniversary of the 2 October massacre in which between 44 and 300 student protestors were killed.
The massacre took place ten days before the Mexico Olympic Games of 1968, when security forces opened fire on a crowd of peaceful protestors, then hastily covered up evidence of their actions.
The exact number of victims remains a mystery. Authorities released 44 bodies, but US Central Intelligence Agency reports estimate the number of deaths to be in the hundreds.
Nobody has ever been prosecuted for the massacre.
Political analyst and Mexico specialist Colin Harding was in the country for the first anniversary of the massacre in 1969 and spoke to witnesses.
"People took refuge in the lifts of apartment buildings...the soldiers came along and just sprayed them with bullets,' he told RFI. "It was the most unbelievable event ... Mexicans have never really got over it."
Thursday's protesters set off from the Square of Three Cultures, where the killing took place in 1968, shouting "2 October is not forgotten". Students drew chalk figures covered in blood stains on the ground to represent those killed.
Amnesty International called on Thursday for the government of President Felipe Calderon to establish the truth behind the massacre, saying it was time for the government to assume its responsibility in the matter.
In 2001, President Vicente Fox created the office of the special prosecutor to investigate crimes which took place during Mexico's "dirty war" against left-wing activists, which began in the 1960s and lasted until around 1980.
The Interior Minister at the time of the 1968 massacre was a target of the investigations. Luis Echeverria was in charge of both the federal police and a clandestine military unit at the time of the massacre. He later became President of Mexico.
Mexican courts have blocked attempts to prosecute him for genocide.