As they cowered in the cold cells of the Navy Mechanics School in Buenos Aires, the political prisoners rounded up by the military dictatorship of 1976 to 1983 would vow, under their breath if they were wise, that one day their captors would pay for their atrocities. Yesterday, they could feel vindication; the cogs of justice had turned.

The conviction and sentencing to life in prison late on Wednesday in Argentina's Supreme Court of Alfredo Astiz, 59, for crimes against humanity committed during the Dirty War, is a signal moment for the country, not least for the time it took to come. The survivors of the school – a concentration camp – had to wait three decades to see punishment delivered, half a lifetime.

If Argentina sometimes faltered on the road to cleansing its national conscience after the darkness of that time – as many as 30,000 so-called political prisoners died at the hands of army and police officers like Astiz, also known as the "Blond Angel of Death" – it has not been alone. Many of its neighbours were also under dictators in those years, suffered the same stains on their national psyches and found it equally hard to know how to erase them.

Just across the Rio de la Plata estuary, Argentina's immediate but much smaller neighbour, Uruguay, has this week taken its own first steps towards coming to terms with what happened within its own borders during its military dictatorship of 1973 to 1985. Congress passed legislation yesterday effectively to nullify a long-standing amnesty for former officers implicated in cases of political torture and murder, opening the way for trials of its own.

It may be that the history books will remember October 2011 as a "Healing Spring" for those populations in Latin America still haunted by the actions of past regimes. The Angel of Death was convicted in Argentina. Uruguay neutered its amnesty laws. And finally Brazil, the largest country on the continent by far, took its own steps towards a first open and honest examination of its past. On Wednesday, its Congress voted to set up a truth commission to investigate rights abuses including those committed during military rule from 1964 to 1985.

That the present in so much of Latin America even now remains tainted by the past will be symbolised by what is coming next in Uruguay and Brazil where the new laws now pass to the desks of their presidents for signature. The emotion will be thick at both ceremonies because this is personal for each of them. President Dilma Rousseff of Brazil spent three years in prison and was herself a victim of torture. Uruguay's leader, President Jose Mujica, spent years behind bars for his guerrilla activities as a former left-wing militant in the 1960s and 1970s.

Unlike its neighbours, including Chile, Brazil has until now shied away entirely from examining the darker corners of its military past. President Rousseff is expected to appoint a seven-member panel to investigate abuses that took place during Brazil's dictatorship. Opposition from the military was set aside after the government promised that alleged abuses committed by rebels during the time in question would also be investigated and a long-standing amnesty for former military officers would not be violated. For that reason not everyone in Brazil is satisfied. "It's a timid commission, much less than those set up in Uruguay and Argentina," said Senator Randolfe Rodrigues of the opposition leftwing Socialism and Freedom Party.

Uruguay is essentially to overturn its amnesty even though its remaining in place was endorsed by voters twice in recent referendums. "This is a historic night," ruling-party MP Luis Puig said after the vote in Congress in Montevideo early yesterday. "The culture of impunity imposed during 25 years must be dismantled and turned into a culture of human rights."

In Argentina, which on Sunday overwhelming re-elected Cristina Fernandez as President, the process is further advanced. In addition to Astiz, 10 other former Argentine military and police officials were found guilty of crimes against humanity and given life sentences. Together, the 11 defendants were accused in a trial that began in 2009 of instigating 86 cases of torture, kidnapping and murder of alleged leftist dissidents who were incarcerated in the Navy Mechanics School.

The school, investigators believe, become a repository for no fewer than 5,000 prisoners of the then dictatorship. Fewer than half of them survived.

The reckoning in Argentina, which has been actively encouraged by President Fernandez since she succeeded her husband, Nestor Kirchner, and came to power four years ago, is not over yet. Still under way in a different courtroom in the same judicial complex is another trial in the case of the alleged systematic theft by the military junta of the babies of young left-wing mothers identified as enemies of the state.

Yet for many, Astiz embodies the worst of what was perpetrated in the name of national security and stability. An ex-navy captain who later would be captured by the British in the course of the Falklands War and repatriated back to Argentina, he became indispensable to his military masters for his ability to infiltrate opposition groups during the Dirty War and then turn in their leaders. His crimes also stood out by virtue of the identities of some of victims. Astiz, who looked ahead without visible emotion when the sentences were read, was accused of participating in the kidnapping and murder of two French nuns Alice Domon and Leonie Duquet as well Azucena Villaflor, a founder of the Mothers of Plaza de Mayo, the group that did more than any other to spark the investigations into the fates of the "disappeared" of the Dirty War.