Almost a quarter of a century after the worst terrorist outrage in Washington DC, the FBI has renewed its investigation into the alleged role of former Chilean dictator General Augusto Pinochet, now held under house arrest outside London.

For years, friends of Orlando Letelier, killed in a car bomb in September 1976 in Washington's Embassy Row, have blamed the general for ordering the former Chilean defence minister's assassination.

Last month, according to sources in a special Radio 4 documentary on the murder, the US Justice Department attached as many as 20 FBI agents and justice to the investigation full-time. The department has never formally closed its files on the case.

Sources quoted in the documentary, called Murder on Embassy Row, say the investigation is being "pursued aggressively" and that the only possible target "is General Pinochet himself".

Notorious bombing

Pinochet's arrest has aroused strong passions

Orlando Letelier had been the Chilean ambassador in Washington under the democratically-elected government of Salvador Allende, which was toppled when General Pinochet led a CIA-backed coup by the country's armed forces in 1973.

An American citizen, Mr Letelier's colleague Ronni Moffitt, also died in the explosion, close to the Chilean Embassy in the heart of Washington's diplomatic quarter.

The notorious car-bombing has been a source of controversy and speculation for years, amid rumours that the American intelligence establishment could have prevented the killings and has covered up evidence that might reveal who bears the responsibility for despatching the bombers to the United States.

I think the current US investigation could come up with enough evidence to prove Pinochet's responsibility for this crime

Juan Garces

Juan Garces, the Spanish lawyer who has been pressing for the general to face trial for alleged human rights abuses, told the programme: "I think the prospects of bringing Pinochet to justice are better now than they've ever been.

"I think the current US investigation could come up with enough evidence to prove Pinochet's responsibility for this crime. My hope is that the evidence will then be brought before a grand jury in Washington."

Warnings 'ignored'

Orlando Letelier was working at a Washington think-tank, the Center for Policy Studies, when right-wing Cuban gangsters detonated a bomb taped under his Chevrolet in a cake tin.

The bomb had been planted by Michael Townley, an American citizen who was working as an international hitman for the Chilean secret police, Dina.

Documents cited in the programme show the State Department and CIA had both received warnings that Dina might be planning some kind of mission on American soil, and friends of Letelier say he was always the most likely target. But they say no special steps were taken to protect him or warn him of any specific danger.

Under a complex deal, Townley was expelled from Chile and found guilty in a Washington court. He was released after five years into a witness protection scheme.

Logic always dictated that this order to assassinate Orlando Letelier came from General Pinochet

Lawyer Larry Barcella

Townley blamed Dina director General Manuel Conteras for ordering the bombing, and in 1993 Contreras was finally jailed by Chile's new democratic government.

Conteras has never said directly that General Pinochet ordered Mr Letelier's murder. But two years ago Conteras finally claimed in a written appeal for leniency that every act he carried out as the head of Dina was in essence directly imparted to him by his Commander-in-Chief General Pinochet.

Leading Washington attorney Larry Barcella, who led the state's case against Townley, is among those now pressing for the case against the General to be actively pursued.

"Logic always dictated ..." Mr Barcella tells the programme, "that this order to assassinate Orlando Letelier came from General Pinochet."

Declassified CIA documents

In an interview earlier this year General Pinochet claimed he had no responsibility for crimes against humanity and torture. He also denied that Dina always acted on his orders. His lawyer declined requests for an interview.

Pinochet ruled Chile until 1990

But a recently declassified CIA briefing paper - quoted in the Radio 4 programme - shows that as long ago as 1978 the CIA believed that not even a majority of the general's own supporters would be willing to swallow claims that Conteras acted without presidential occurrence.

The paper is one of thousands on US-Chile relations in the 1970s recently made public on President Clinton's orders. The papers confirm suspicions that the Nixon administration knew of the Pinochet regime's human rights abuses.

Together with other declassified documents they reveal the administration was warned of rumours that Chile and other Latin American regimes were joining forces to murder opponents abroad in a project codenamed Operation Condor.

When these documents are declassified ... we will know the essence of General Pinochet's role in authoring this extraordinary act of international terrorism

Peter Kornbluh

However almost all the papers that bear directly on the Letelier affair have been withheld, apparently because of the ongoing investigation, and many others have been heavily censored.

Peter Kornbluh of the National Security Archive, an independent research organisation, told the programme: "We have never seen the CIA documents on this case ... I believe that when these documents are declassified, and they absolutely must be declassified, we will know the essence of General Pinochet's role in authoring this extraordinary act of international terrorism."

Serious threat to Pinochet's liberty

The Justice Department has declined to give any further details of the investigation, but it is believed its agents have travelled both to Chile and to Florida where a Cuban criminal involved in the murder is in jail.

One cynical interpretation is that the renewal of the case is a political attempt by the Clinton administration to embarrass George Bush Junior, the Republican presidential candidate whose father George Bush was the director of the CIA at the time of the Washington car-bombing. It has never been known how much - if anything - the future president knew about Dina's clandestine operations abroad.

I don't want revenge, simply for the whole truth to be told at last

Orlando Letelier's widow Isabel

If FBI agents do gather enough evidence to indict General Pinochet, the Letelier-Moffitt investigation could yet be the most serious threat to his liberty. If he is extradited to Spain to face charges of torture and conspiracy to torture, he is likely to be released even if found guilty - Spanish law limits the scope of its courts to jail people in their eighties.

Orlando Letelier's widow Isabel tells Murder on Embassy Row she has been hopeful the mystery of her husband's death will finally be resolved ever since General Pinochet was arrested in Britain.

"When I heard the news I said that finally there may be a little bit of justice. I was exhilarated ... I don't want revenge, simply for the whole truth to be told at last."

Murder on Embassy Row is being broadcast on BBC Radio 4 at 20:30 GMT on 9 December