When the cycle comes around to commemorate the spectacles of 1968 in Chicago, Paris or Prague, few people outside Mexico remember that the real bloodbath that year was in Mexico City.

It is not the hands wearing black gloves held aloft by American athletes at the Olympics that year, but the white gloves of the army’s Olympia Brigade, which fired upon crowds of students and families in the Tlatelolco district of Mexico City, killing 350 people in cold blood, that will be recalled.

This was the quintessence of political violence in Mexico for decades, between the state and the leftist opposition. These were the faultlines which detonated the Zapatista movement in Chiapas during the mid-1990s, the mobilisation of workers in wretched sweatshops along the US border, the near rise to power of leftist López Obrador in his 2006 electoral bid.

Only since that year has ideological violence been subsumed by the savagery of the war of narco cartels between each other and, so it is claimed, the state.

Into this narrative enters the likelihood – now confirmed by both the attorney general of Guerrero state, Iñaki Blanco, and the Guerreros Unidos cartel in his territory – that some, if not all, the students arrested during the Ayotzinapa protest were handed over by police to the cartel for summary execution. Inevitably the barbaric procedure invokes protest in the streets that echoes 1968: crowds occupy the famous Zócalo plaza and set the door of President Peña Nieto’s national palace ablaze.

But the significance of these savage executions – bodies tortured and torched or dumped in a river – lies in the entwining of ideological and narco violence: two nightmares, two perfidious calculations, in one.

Mexican governments – under presidents Vicente Fox, Felipe Calderón and now Peña Nieto – have tried to present their war against the narcos as a state apparatus against organised crime. This is also the bleat of the US as it provides “aid” for the “war on drugs” while also exulting in the opportunities for “investment” in Mexico. Britain also blathers on about “trading opportunities” with Mexico and support for its fight against crime. We must buy the lie, continue the pretence.

However, for a long time the world’s bravest reporters have challenged this version of events. Mexico’s leading writers, Lydia Cacho and Anabel Hernández, received serial death threats for proving that the authorities – politicians, police, army – are synonymous with the cartels or in league with them.

Others on the left have always asked, to general derision: where are the armed forces in all this? What connects the state violence of the 1960s to the narco war? The late Charles Bowden, America’s great writer on the border, wrote of “the biggest cartel in Mexico: the Mexican army”. Julián Cardona, the great chronicler and photographer of the narco war in Ciudad Juárez during its grim primacy as the world’s most dangerous city, always said that the same hand of state behind violence against the left was at play among the drug lords.

Lesser writers on Mexico, including myself, have insisted that the line between legitimacy and criminality, upon which Mexico’s international relations are based, is a fantasy, that the line between legality and illegality is a lie, not only within Mexico, but internationally, with regard to the laundering of the profits of crime.

The Mexican state, however, continued with such language as that of General Jorge Juárez Loera, commander of the 11th Military Region, who told a press conference in Chihuahua in 2008: “I would like to see the reporters change their articles and where they say ‘one more murdered person’ instead say, ‘one less criminal’.”

Now we can see the arguments advanced by Cacho and Hernández, Bowden and Cardona, utterly vindicated by, in their way, the most shocking of many appalling mass murders that have taken the death toll past 100,000 since 2006, with 20,000 missing. Shocking, because it is now brazenly clear that the Mexican state and cartel death squads are as one.

Until now perhaps the most poignantly innocent victims in any single massacre were 72 migrants from Central America summarily executed in 2010 for failure to pay added fees to their traffickers, probably the Zetas cartel. Now these young people are kidnapped from their village of Ayotzinapa, near the tourist resort of Acapulo, by police from nearby Iguala, apparently on instructions from the mayor, worried that a protest might spoil a public event hosted by his wife. That is now a capital offence in Mexico, as it was to protest in 1968. The difference is that the state need not trouble itself to be the executioner. Unlike the white-gloved fingers of the Olympia Brigade, hardened cartel torturers and hitmen now pull the trigger. For their services, the cartel can expect a handsome payment in kind – and they will get it.