By Daniel Schweimler BBC News, Buenos Aires

Relatives of those rounded up have long fought for justice

Argentina's ex-President Raul Alfonsin has appeared in court to defend a law that let murderers and torturers from the former military government go free.

Mr Alfonsin was the only witness for the defence in the retrial of a former police chief, Miguel Etchecolatz.

Etchecolatz was sentenced to 23 years in prison in 1986 for crimes against humanity, but was freed after a few months because of an amnesty.

He is the first government figure to be retried since the amnesty was scrapped.

The laws were last year ruled to be unconstitutional.

For many in Argentina, the ghosts of the past have still not been put to rest.

When seven years of military rule ended in disgrace in 1983, hundreds of people were tried and sentenced for the kidnap, torture and killing of tens of thousands of perceived opponents of that government.

Raul Alfonsin headed the first civilian government charged with the task of rebuilding Argentina after the darkest period in its history.

Under pressure from the military and wanting to leave the past firmly behind a traumatised nation, he passed the law of due obedience.

That and other subsequent laws in effect let the convicted killers and torturers go free.

Long campaign

Mr Alfonsin defended his actions in court, saying that under intense pressure, he did what was necessary for Argentina at the time.

Miguel Etchecolatz was freed a few months into his sentence

"We'd started work on a human rights project that was without parallel in the world, but obviously the military situation was very complicated," he said.

The former police chief in the city of La Plata, Miguel Etchecolatz, was one of the beneficiaries, serving just a few months of his sentence for 91 counts of torture.

But the families of the estimated 30,000 victims of that military government and those who survived the torture continued their campaign for justice and last year, Argentina's supreme court overturned Mr Alfonsin's law, ruling it to be unconstitutional.