When Joan Jara went to identify the body of her husband, Victor, she found it riddled with 44 bullets and dumped among a pile of corpses in the Santiago morgue. The poet's wrists and neck were broken and twisted. Where his belly ought to have been was a gory, gaping void.

The memory of that grim scene soon after the Chilean coup – on 11 September 1973 – is still painful for Jara, but it is not the only cause of her grief. The prime suspect in the killing, a former lieutenant in the Chilean army, is still alive and at liberty in the US, where he has citizenship through marriage.

Now the campaign to extradite him to his homeland has taken a step forward after Pedro Barrientos Nuñez, who lives in Florida, was served notice of a lawsuit in the US accusing him of torture, extrajudicial killing and crimes against humanity.

It is not the only quest for justice in Chile that dates back to the dark days, weeks and years following General Augusto Pinochet's ousting of socialist president Salvador Allende. Thousands were executed or made to disappear, and thousands more tortured after the CIA-backed military takeover.

But Jara – folk-singer, theatre director and cultural ambassador of the Allende government – remains arguably the best-known victim and a potent symbol of a nation still struggling to find peace with itself more than two decades since the return of democracy.

It is his final poem – smuggled out from the stadium where he was incarcerated and killed – that adorns the entrance to Santiago's Museum of Memory. It is images of his face on banners carried by a new generation of student protesters and it is his music that will be played on radio station and in folk clubs as a nation remembers the tumult of the coup.

Jara was born in 1932 into a poor rural family, where he learned Chilean folk traditions from his mother. He mastered the guitar and piano and developed a reputation as a singer and songwriter and leading light in the Nueva Canción Chilena (Chilean New Song) movement. He met British-born dancer Joan in 1961, when she was teaching at the University of Chile."He came to see me with a little bunch of flowers that he probably stole from the park, because he never had any money," she recalls.

Jara put the theatre aside in 1970 to focus on music and to campaign for Allende, organising rallies, playing free concerts and writing songs about social injustice and the lives of ordinary Chileans.

Allende won the election, but faced the enmity of the Chilean right, and the US government, even before he took power in October 1970.

Declassified official US documents from that period show the CIA planned a coup almost as soon as Allende won the 1970 election. When he was finally ousted, US secretary of state Henry Kissinger spoke of the covert pressure Washington had applied, saying to president Richard Nixon: "In the Eisenhower period, we would have been heroes."

As a voice of the left, Jara was also the target of death threats. "His last songs are somehow strangely prophetic. Victor knew what was coming," Joan says.

On the day of the coup, Jara was due to perform at the state technical university, where Allende was planning to announce a plebiscite. It never happened. Rumours that the military would step in had circulated for some time, but the violence still took many by surprise.

The current Chilean presidential candidate Michelle Bachelet, who was then a student militant, recalls her father, an airforce general, being woken up at 4am by a phone call from a friend asking him if the military were about to take control.

"My father said 'Don't worry. Go back to sleep.' But it nagged him. He went out and saw all the cars missing in the generals' barracks and then he realised something was up," she said .

That morning, La Moneda, the presidential palace, was shelled by tanks. At noon, it was stormed by the military. Allende refused to surrender and killed himself before troops arrived.

"Victor and I listened together to Allende's last speech," Joan recalls. "Then we saw how one radio station after another replaced normal broadcasting with military marches and pronouncements."

Victor left Joan to join students defending the university. "I didn't look at him leave. It didn't seem important. I said goodbye in an ordinary way. That was the last I saw of him," she says.

Jara was among those rounded up by the military and taken to a stadium that had been turned into a makeshift prison camp. When Joan went to the British embassy for help, it was closed (though many other nations had opened their doors to asylum seekers). Victor managed to smuggle a message out of the stadium, telling Joan where he had last parked their car and saying that he loved her. That was the last she heard from him.

A week later, she was taken to the morgue and asked to identify his body. "Victor was among hundreds of bodies that were literally piled up; all with horrible wounds. Some with their hands tied behind their backs."

Despite what she saw, Joan considers herself fortunate. "I was lucky to be able to identify the body and come to terms with what they had done to him and that he was really dead."

According to Chile's truth and justice commission, 3,095 people were killed during the 1973-90 Pinochet dictatorship, including about 1,000 who "disappeared". Bodies are still being found today.

It was only last December that Barrientos and another officer were charged with Jara's murder and five others were named as accomplices. Lawyers said the case was based on the corroborated testimony of a conscript, Jose Paredes, who had earlier been accused of the killing.

The suit filed against him in the US last week invokes the Torture Victim Protection Act and the Alien Tort Statute, which gives US courts jurisdiction over rights violations committed in other nations.

It alleges that Barrientos ordered the torture of the poet in the stadium locker room and then played Russian roulette with Jara, shot him in the back of the head at point-blank range and ordered five conscripts to fire dozens of rounds into the body.

Barrientos has denied the accusations. "I do not need to face justice because I have not killed anyone," he told a TV crew that turned up at his home in Deltona, Florida, last year.

History remains fiercely contested in Chile. Santiago's museum, anniversary events and flood of related TV dramas and radio programmes attest to the growing recognition of the atrocities carried out during the Pinochet era. This week, the Chilean judges organisation made an unprecedented apology for its failure to protest human rights abuses during the Pinochet era.

But many of the general's former supporters argue the events of 1973 are now misrepresented. "Political parties have demonised anything vaguely related to the military government. People talk of abuses of human rights, but that is wrong," said Roberto Mardones, the administrator of the Pinochet Foundation, which has an exhibition of the general's medals and books (many on Napoleon) and a mock-up of his office.

"In 1973 citizens were desperate for change. There was a lot of hate. There were strikes, shortages of gas, sugar, matches and nappies. When the junta proclaimed on the radio that they would bring peace and stability, there was euphoria. I went out with my family to celebrate. It was like a carnival."

The gulf between such views and those of the victims shows the difficulty of reconciliation in Chile after 40 years.

Joan Jara said the US could now help by recognising its role and supporting efforts to bring the accused to justice.

"I appeal to people in the United States to put pressure on their government to respond to our appeals," she says. "The coup was supported and financed in part by the CIA so the American government at that time had some responsibility for what happened. I know many in the US condemned the coup and were in solidarity with the people of Chile and the victims of executions, disappearances and torture. This case is for all of us."