Scottish and American indictments allege that two Libyan security officers were responsible. Since November 1991, Colonel Gaddafi has refused to extradite them to face trial in Scotland.
The international arguments have been propelled directly into the lives of the Lockerbie families. A company owned by Lonrho and the Libyan Arab Foreign Investment Company (Lafico) decided to produce a documentary which lawyers for the relatives of the American dead allege is likely to become part of a propaganda campaign to suggest that the charges are part of a Western conspiracy.
Alan Francovich - a fast- talking and nervous film-maker from Los Angeles, who is now based in Belsize Park, north London - was put in charge. He has been arriving at relatives' homes, exuding an apparently genuine air of sympathy.
Lee Kreindler, who heads the legal team for American relatives, said Francovich had tried to win over the families by saying he was a friend of John Merritt, an Observer journalist greatly respected by the relatives of the dead for going to the United States and testifying on their behalf when he was in the final stages of leukaemia.
Francovich absolutely misrepresented himself to us,' Mr Kreindler said. 'He did not mention any link with Libya.
'We were quite willing to help him make his film, until we found out about the money,' added Dan Cohen, whose daughter Theo died at Lockerbie. 'The fact that he kept quiet about his backers means he is completely discredited in my eyes.'
But not everyone has turned the producer away. Jim Swire, the leader of the British relatives, who has become suspicious of official explanations partly because of the failure to hold any public or Parliamentary inquiry in Britain, said the American was visibly shaken by the sight of his daughter's grave when they met last year.
'He was clearly moved by the Swire family story,' Dr Swire said. 'He told me his life was in danger but that he wanted to do everything possible to find the truth. I liked the chap.'
Francovich runs Hemar Enterprises in Kilburn which is owned by Metropole Hotels, which in turn is two-thirds owned by Lonrho and one-third by Lafico. Metropole's directors are 'Tiny' Rowland, Lonrho's chief executive and former proprietor of the Observer, Ken Etheridge, Lonrho's head of security, and Smeida el-Naili, a director of Lafico.
After the Libyan involvement in the firm was revealed in the press in November, Lonrho announced in January that it would withdraw support and said it would use copyright law to ensure the film was never shown.
But the Hemar Enterprises offices are still open and Francovich says the film - The Maltese Double Cross - will be shown across Europe in the spring. He refuses to discuss where the money for the project is now coming from, but promised that none of the information he has collected, believed to include the transcript of a Scottish police interview, will be handed on to Libya.
For American relatives the concern about the film is wider than a dislike of what they inveitably see as a Libyan propaganda ploy.
They fear it will thicken the fog of competing conspiracy theories and assertions of guilt and innocence which have covered the Lockerbie case. 'We saw Clinton on the fifth anniversary in December last year and I told him it's getting like the who-killed-Kennedy industry,' said Susan Cohen, Dan Cohen's wife. 'At times it seems like every nut and hoaxer in America is jumping on the bandwagon.'
Francovich does not behave like a sinister man. He will not allow his photograph to be taken, because he says he is frightened that unspecified powerful people want him dead. But he still talks reasonably freely.
'We will show that the US government knew Pan Am 103 was going down and did nothing about it,' he said. 'The first people on the scene (at Lockerbie) were from the CIA and they removed evidence. They knew that drugs were going through Frankfurt. The Scottish police were never allowed to conduct an independent investigation.'
This 'drugs theory'is not new. It has been popping up all over the world for at least three years.
According to the story, there was a CIA or US Drugs Enforcement Agency (DEA) drug-smuggling route running from Lebanon to New York via Cyprus and Frankfurt. Pan Am 103 was blown up because a terrorist cell from the Popular Front for the Liberation of Palestine - General Command (PFLP-GC), whose members were rounded up by the German authorities and then released just before the bombing, switched the suitcase containing heroin for the bomb. A variant holds that the rogue, drug-smuggling US agents blew up the plane to kill good US agents who could expose them.
The latest published version has come from Lester Coleman, a low-level DEA informer in Cyprus in the early 1980s, in his book Trail of the Octopus.
The problem for conspiracy theorists is that Coleman is a compromised figure. Leaving aside the fact that he is wanted in the US on passport fraud charges, sceptics have pointed out that his views suited two vested interests very well indeed.
Any evidence which can pin blame on the US government for the bombings would not only help the Libyans but also Pan Am's fight against compensation claims from the relatives.
If the CIA or any other agency was involved, the airline could argue, it should be the US government that foots the bill.
Documents filed during the court hearings included a letter from James M Shaughnessy, Pan Am's lawyer, stating that Coleman had been in the pay of Pan Am. He received dollars 47,000 for his work on developing the drugs theory, which he and an associate, Juval Aviv, helped place in several American newspapers and magazines before his book was published.
'The Coleman and the Francovich scenarios are just rubbish and propaganda,' claimed Lee Kreindler. ''There is just not a shred of evidence. In the end Pan Am could not mention the drugs theory in court. They knew we would have taken them apart if they had.'
If the drugs theory is one side of the coin, the British and US authorities' unshakeable belief in the strength of their case against Abdel Basset Ali al-Megrahi and Lamen Khalifa Fimah, the two Libyans accused of placing the bomb in an unaccompanied suitcase in Malta which was tagged to be transferred on to Pan Am 103 at Frankfurt, is the other.
Privately, the authorities admit that after Syria's support for the West in the Gulf war it may seem convenient that two Libyans rather than members of the Syrian-backed PFLP-GC are wanted to stand trial. But Scottish police were first linking the bomb with Malta and therefore the two Libyans in 1989, two years before the war.
Intelligence officers have speculated that when the cover of the terrorists rounded up in Frankfurt was blown, they may have passed on the operation to the Libyans, or the Libyans may have taken advantage of the fact that the finger of guilt would point to the Palestinians and acted on their own.
Vincent Cannistraro, the former head of the Lockerbie investigation for the CIA, said last week: 'The investigation has been driven by the collection of forensic evidence, not intelligence. Almost all of the major developments have come from laboratory analyses which did not and do not lend themselves to politicking. All this drugs stuff is total fabrication. We never found anything to do with drugs.'
Last year it appeared that claims from the Swiss company Mebo, which unwittingly made the timer for the Lockerbie bomb, could undermine the Scottish case. The company said it had also sold timers to the East Germans, who were in contact with the PFLP-GC. But the company has since admitted that it has received 'legal, travel and other expenses' from Libya while collecting evidence which could help the accused pair.
The investigators treat the Mebo issue with contempt. 'We allege that the circuit boards can be shown in court to be one which was sold to Libya not East Germany,' said Mr Cannistraro. 'And in any case the circuit board evidence is not central to our case.'
The bitter debate, the accusations of official connivance in the murder of 270 people, and the counter-charge of collaboration with Libyans, has led to relatives fighting each other.
Dr Swire has been to Libya and met Colonel Gaddafi. Last month, Gaddafi approvingly quoted Dr Swire's support for the two Libyans to be tried at an international court in the Hague rather than Scotland.
In December Dr Swire was quoted in the Guardian as saying that he 'had good reason to believe Coleman's drug theories' even though they provided an escape route for Pan Am's lawyers. 'We may be faced with the decision of whether we want the money or the truth,' he said.
A horrified Daniel Cohen saw the article. 'I know of no one, no one, who would ignore the truth about the murder of a child or husband or wife or brother or sister just for money,' he said in a letter to Dr Swire. 'Yes, governments lie. Your government lies and my government lies. But lawyers for insurance companies also lie, so do shady low-life fugitives and weepy TV producers. If you can't see that, you can't see anything.'
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