I came to Guatemala in the late 1980s as a young researcher for what was then called Americas Watch (now Human Rights Watch). Back then, the human rights community in Guatemala was under enormous pressure. A civil war was still very much underway. And the idea that a former president might be put on trial for genocide seemed unlikely.

Times have changed. This week, a former president and his chief of military intelligence are on trial in a Guatemalan court for genocide and crimes against humanity.

In 1988, many countries in this hemisphere were just beginning to contend with abuses of the past, and for most, prosecution seemed out of the question. Truth commissions, essential though they were, were seen to be as far as governments would go in addressing the past.

Only Argentina had tried to prosecute former leaders for rights abuses, trying nine (and convicting five) members of its former military junta in 1985. But new laws effectively put a stop to any further prosecutions of abuse. Most of the nearly 9,000 disappearances documented in the Argentinean truth commission’s final report went unpunished.

But over the next quarter century, we have seen astonishing progress in the search for accountability throughout the hemisphere. Jo-Marie Burt, of George Mason University, has written extensively about the transformation of recent decades, including in her recent article, “Challenging Impunity in Domestic Courts: Human Rights Prosecutions in Latin America.”

In Argentina itself, in 1998, a judge held that amnesty laws did not apply to the crime of baby kidnapping. In 2005, after years of petitions, agitation, and legal battles by victims’ rights groups and their supporters, the Supreme Court declared the amnesty laws as such unconstitutional, and prosecution became a real possibility again. To date, more than 1,500 alleged perpetrators have faced prosecution in Argentina; more than 200 having been convicted.

In Chile, it was only after General Augusto Pinochet left power in 1988 that a truth commission became possible. Although the commission documented more than 3,000 murders and disappearances, a 1978 amnesty law continued to block most prosecutions long afterward.

Pinochet’s arrest in London in 1998 and the House of Lords’ vindication of the principles of accountability galvanized the filing of numerous criminal complaints against the former dictator in Chile, where he returned in March 2000. But that August, pushed by family members of victims, the Supreme Court held that the amnesty did not apply to the crime of forced disappearance, allowing prosecutions to advance.

Pinochet eventually died in 2006 without having been tried. But since 2000, more than 750 members or former members of the state security forces have been prosecuted for human rights violations.

In Peru, for years, cases brought to the courts on behalf of civilian victims of abuses committed during the country’s two-decade long civil war were blocked by amnesty laws and an unreceptive system of military justice. Change came with the thorough documentation of the Peruvian Truth Commission—which issued its final report in 2003—and several key judgments by the Inter-American Court, which found state responsibility for human rights violations, and struck down the amnesty laws. In December 2009, the Supreme Court upheld the conviction and 25-year sentence of former president Alberto Fujimori for grave violations of human rights.

Significant barriers remain in Peru. Comparatively few registered complaints have as yet been processed, faced with a sluggish criminal justice system and political hostility by the government in power from 2006 to 2011.

In Uruguay, in 1986, a year after the end of military rule, the first trial of a military officer accused of human rights abuse was blocked by a new law which effectively halted prosecutions of members of the security forces accused of human rights violations.

The Inter-American Commission’s call for repeal of the law went unanswered until persistence by victims’ groups led some judges to reinterpret the law and allow some prosecutions to proceed.

In 2010, former president Juan Maria Bordaberry was convicted and sentenced to 30 years in prison for violation of the constitutional order, as well as for murder and disappearance.

In each of the above cases, what at first seemed an impossibility—prosecution of former senior figures for grave crimes—became a reality within the space of two or three decades.

Many factors were at work, but three stand out: pressure and persistence by victims and their families, supported by human rights organizations; secondly, a capable cadre of lawyers, judges and prosecutors skillful at exploiting political openings when they occur; and thirdly, the role of the Inter-American Commission and Court in providing redress when domestic avenues are shut.

The story is not all positive. There are numerous examples of international crimes still unpunished, where the political will, or the necessary laws or legal institutions are lacking. Haiti’s former president Jean-Claude “Baby Doc” Duvalier has yet to face trial for crimes committed during his rule.  Brazil has not prosecuted a single military officer for crimes which took place during the 1964-85 dictatorship. Just last month, Uruguay’s Supreme Court held that a law allowing fresh investigations of dictatorship-era human rights crimes violates the country’s constitution, a ruling that puts dozens of cases into doubt. And in the United States, President Obama, has refused to countenance prosecutions for crimes of torture or forced disappearance which took place under his predecessor.

Prosecutions are not the only appropriate response. But, together with truth, reparations and institutional reform, they are an essential part of a comprehensive approach to transitional justice.

Guatemala now  stands at an important crossroads, and is poised to join the growing list of countries which, over the past two decades, have begun the hard but necessary process of coming to terms with a scarred past.

In the months ahead, advocates for justice across the globe will be looking to Guatemala for a signal that, after decades of impunity, a new stage in the struggle for justice has emerged.

James A. Goldston is executive director of the Open Society Justice Initiative.