Last week it was solved. The 'Danish photographer' who smuggled in the remote-controlled bomb in a camera bag was identified as Roberto Vital Gaguine, a militant of the Argentine People's Revolutionary Army (ERP). In 1984, Gaguine was part of a clandestine 15-man team working for Nicaragua's left-wing Sandinista government.
One of those who has devoted years to trying to uncover the identity of the La Penca assassin and his paymasters is a British victim of the bomb, Susan Morgan. Like many others who entered the maze of rumours, she came to suspect the CIA, or one its many proxies. Now living in London, she admitted last week that the revelation of Gaguine's identity was a shock, but that it did not resolve the central mysteries of La Penca: who was the paymaster and what was the motive?
Pastora was a man with many enemies. He had been a flamboyant hero of the Sandinista revolution, but quarrelled with the leadership and took up arms against them. They wanted him dead. The US-funded Contras, nominally Pastora's allies in the war against the Sandinistas, also hated him for his refusal to take their orders. In 1984, as the CIA struggled to unite the factions, Pastora was the main obstacle.
When he suddenly called a press conference at his base in the jungle along the Nicaragua-Costa Rica border, the press corps went along. Among them was a man identified by his passport as Per Anker Hansen, a Danish photographer. Tall, with chestnut hair and green eyes, Hansen was accompanying a Swedish film director, Peter Torbiornsson.
After the bombing, Torbiornsson told investigators that he had first met Hansen six weeks before the bombing, when they stayed in the same hotel in Costa Rica. Recently, however, after nearly nine years' silence, Torbiornsson admitted that he had seen Hansen in the Nicaraguan capital of Managua in the company of a known Sandinista counter-intelligence agent. When Pastora called his press conference, Torbiornsson agreed to take Hansen along.
Hansen claimed to have been injured in the explosion and was treated in hospital for shock. At dawn the next day he discharged himself and disappeared. Last week, close relatives of Gaguine identified the photograph of Hansen as Gaguine. The final proof came when a set of fingerprints, known to belong to the bomber, were matched with Argentine police records of Gaguine's prints.
Gauguine's family knew nothing of his involvement with La Penca, but others have furnished details of his life: he came from a middle-class family and his ERP nom de guerre was Martin el Ingles. He arrived in Britain in 1978, where he later applied for asylum. By 1980 his whereabouts were again unknown.
He will never be brought to justice: in 1989, he died, with 18 others, in a guerrilla attack on an army barracks on the outskirts of Buenos Aires.
At one level, the mystery now seems to be resolved: if Gaguine was working for Sandinista intelligence, it seems clear that the Sandinistas were the authors of the crime. But such was the tangle of inter-penetration and disinformation in the intelligence war in Latin America in the Eighties that there can be no certainty.
Enrique Haraldo Gorrioran was the commander of the ERP cell in Managua, and ordered the fatal barracks attack, but he did not take part. Former ERP guerrillas are convinced that he was a double agent. The evidence is persuasive: he repeatedly escaped from incidents in which many of his companions died, and the police often seemed well-informed about operations he ordered. Police sources say he is now living in Brazil on the proceeds of of kidnappings and bank robberies.
Gorrioran would also have been in immediate command of the La Penca bombing. The question that remains is how far up the Sandinista power structure the chain of command went in controlling groups that worked for them? The former Sandinista interior minister, Tomas Borge, an implacable enemy of Pastora, has denied that the Sandinistas were responsible for La Penca. But he did not rule out the possibility that 'rogue Sandinista elements' might have been involved.
In a recent history of the Latin American intelligence war, two Argentine journalists claim that the ERP group had been penetrated by Chilean intelligence and, by extension, the CIA.
This could explain the strange behaviour of the CIA over La Penca. An atrocity on this scale, perpetrated by the Sandinistas, and in which a US journalist was murdered, offered them a propaganda bonanza, yet they never exploited it. Instead, there was evidence of a CIA cover-up: vital forensic evidence was removed to CIA headquarters in Virginia and never returned.
For the victims of La Penca, the revelation of Gaguine's role is a huge step forward. But, as Susan Morgan said yesterday: 'This is not the end of the story. It is just the beginning of a new phase.'