This is a tale of Chile, a suicide, a poet, and poison, more or less in that order.

It is also a story of calendars and conundrums.

For example: How did Marxist president Salvador Allende really die?

Or: Who killed Pablo Neruda?

No sooner is one riddle solved in the world’s most attenuated land than another one rears its equally mysterious head.

This country’s brooding worries are never closer to the forefront of national angst than they are now, in early September, as el once approaches yet again.

Pronounced “el own-say,” the word means “the eleventh,” and mark a date that much of the world knows as 9/11, the anniversary of the terror attacks that claimed nearly 3,000 lives in New York City and near Washington, D.C., on that terrible day in September, 2001.

But, in Chile, the 11th of September — el once — is the anniversary of the coup that overthrew peaceful revolutionary Salvador Allende in 1973, ending three years of turbulent but democratic revolution and triggering 17 years of unflinching military dictatorship under Gen. Augusto Pinochet.

Even now, nearly four decades later, the date still stirs bitter memories among Chileans, reopening old wounds and figuratively raising the dead, including more than 700 presumed victims of a military rule whose fates have yet to be fully resolved. In all, about 3,000 Chileans were murdered or “disappeared” in the years that followed the coup.

El once remains a freighted anniversary, not only for older people with clear personal recollections of that day, but also for many who were not yet born in 1973, including tens of thousands of present-day students and labour activists who, for months, have been staging angry anti-government demonstrations, protesting against long-standing inequities in the country’s education and health-care systems.

“In Chile, political alignments run in families,” says Judith Teichman, a University of Toronto political scientist and an expert on Chile. “The historical memory is passed on.”

Along with the riddles.

For example: how did Allende die?

For decades, Chileans on both sides of the country’s stubborn ideological divide have debated the question with venomous passion.

The original military version of Allende’s death was that the socialist president took his own life, shooting himself through the head with an AK-47 assault rifle as the Chilean Air Force bombed the presidential palace, known as La Moneda, and as army tanks pounded the building at the height of the fighting on the day of the coup.

But supporters of the 65-year-old martyr have long insisted that Allende was murdered, gunned down by troops under the command of Pinochet, who had taken over as commander of the armed forces only about two weeks earlier but who would go on to rule the country with an iron fist and an unrelenting neo-liberal economic program for nearly two decades.

“This was an extremely evil government,” says John Dinges, a professor of journalism at Columbia University and author of a book on terrorist tactics under military rule in Chile. “Pinochet was not the worst, but he was among the worst.”

Almost no one on the left believed the military account of Allende’s death. The conviction that the president was murdered survived largely intact even after Chilean physician Patricio Guijón, an Allende supporter, declared that he was present and saw the president shoot himself with a rifle — a gift from Cuban leader Fidel Castro — that he held clutched between his knees as he squeezed the trigger.

The extended Allende family has long accepted this version of events, but still the controversy persisted.

A little more than a year ago, in May 2011, a Chilean judge named Mario Carroza ordered that Allende’s body be exhumed for examination, in hopes of resolving the debate once and for all.

An international panel of medical experts, including a Spaniard and a Briton, decided in July 2011 that the original military account was in fact accurate. Allende shot himself.

You might have thought that this finding would have ended the debate, and for most people it probably has.

“I can understand if he killed himself,” says Larry Birns, director of the Council on Hemispheric Affairs, a Washington-based think tank. “He was a hero. He could have got a deal to leave the country. But he remained in La Moneda.”

Still, at least some Chileans remain stubbornly convinced of Allende’s murder, while others have shifted the controversy to another notorious death, that of poet and Nobel laureate Pablo Neruda, a lifelong communist who fervently supported Allende’s socialist government but who died of prostate cancer at age 69, just 12 days after the 1973 coup.

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At least, that is the official version.

This past December, the Chilean Communist Party petitioned to have Neruda’s body exhumed in order to address persistent rumours that the giant of Latin American and world literature was in fact poisoned by agents acting on Pinochet’s behalf.

Carroza, who is charged with investigating more than 700 as yet unresolved coup-related deaths, has yet to rule on the request, which has been fuelled in large measure by claims from Neruda’s one-time driver, Manuel Araya, that the poet was alert and in no evident peril on the day of his death.

Anaya speculates that Pinochet agents snuck into the Santiago clinic where his employer was receiving routine treatment for his prostate condition, injecting him with a drug that induced a heart attack.

Those claims might seem far-fetched in some countries, but they sound much less so in Chile as it was during Pinochet’s rule, when no small number of the dictator’s enemies perished in a similar fashion. These apparently included former president Eduardo Frei Montalva, who is widely believed to have been gradually poisoned to death by Pinochet agents at a Santiago medical clinic in January 1982.

Columbia University’s Dinges says that he, for one, does not dismiss the allegations about Neruda.

“To say that Neruda may have been poisoned, it’s certainly worth checking out,” he says. “The background makes me think it should be checked out.”

Meanwhile, a determined protest movement continues to storm the streets of Chile’s main cities, 22 years after the end of military rule and six years after Pinochet’s death.

Led mainly by students, the protesters are demanding reforms to the dual-track nature of social institutions in Chile, where the rich and upper-middle class attend expensive private schools and receive medical treatment in private hospitals, while the poor and lower-middle class are stuck with shabby, underfunded state-run services.

With its vineyards, orchards and copper mines, Chile is among the most prosperous countries in Latin America, but that achievement holds few benefits for the poor in what is also among the most lopsided economies in the region.

“The working class don’t have any chance of university,” says Teichman at the U of T. “If you are born into the working class or the lower-middle class in Chile, you are stuck there.”

The two-track system of social services was instituted under Pinochet, but a succession of centre-left governments did little to restructure the economy’s underlying inequities following the country’s return to democracy in 1990.

Two years ago, billionaire businessman Sebastián Piñera was elected president, marking a peaceful return to conservative rule, a transition widely seen as a victory for Chilean democracy but one that has done little to improve conditions for the country’s less privileged.

“Piñera has made no effort to open up the portals of Chile’s social institutions and let the poor people in,” says Birns at the Council on Hemispheric Affairs.

Meanwhile, el once approaches yet again, and a dead poet, a dead president, and hundreds of as yet unredeemed martyrs shift uneasily in their graves.