The Lockerbie bombing was ordered by Iran and carried out by Syrian-based extremists, a former Iranian intelligence officer has admitted, shining new light on Britain's worst terrorist atrocity.
Abolghassem Mesbahi, who has defected to Germany, said Pan Am flight 103 was downed in 1988 in retaliation for an American navy strike on an Iranian commercial jet six months earlier, in which 290 people died.
He claimed that Ayatollah Khomeini, who was Iran's supreme leader at the time, ordered the bombing "to copy exactly what happened to the Iranian Airbus".
His testimony throws into doubt the conviction of Abdelbaset al-Megrahi, the former Libyan intelligence officer jailed for the bombing. It also suggests that Libya was not the driving force behind the attack.
Sources also said that the bomb was placed on board Pan Am flight 103 at Heathrow, not in Malta, as the prosecution in Megrahi's trial claimed.
Previously unseen evidence gathered for Megrahi's aborted appeal supports Mesbahi's claim and suggests that the bombers belonged to the extremist group the Popular Front for the Liberation of Palestine - General Command (PFLP-GC).
Documents obtained by Al Jazeera television for a documentary name individuals said to be involved in the bombing, including the alleged bomb-maker, the alleged mastermind and the man who may have put the bomb on the Boeing 747.
The evidence adds weight to claims that the truth was covered up by Britain and the United States because they did not want to antagonise Syria, a key power on the doorstep of Saddam Hussein's Iraq.
Megrahi, the only man convicted of the bombing, dropped his appeal when he was granted compassionate release from prison in 2009 because he was suffering from cancer, but protested his innocence until he died in May 2012.
Ever since his conviction in 2001, there have been claims that he was the victim of a miscarriage of justice, and many of the families of the 270 people who died believe the true story has never been told.
Two British film-makers, Bill Cran and Christopher Jeans, who have spent the past three years investigating the Lockerbie bombing, were given access to the defence material by Megrahi, who hired a former Manhattan district attorney to review his case and gather new evidence.
Megrahi's conviction was based on the theory that Colonel Muammar Gaddafi ordered the attack in retaliation for the 1986 American bombing of Tripoli and Benghazi. But the documentary claims that it was in fact an act of revenge for the loss of Iran Air flight 655 in July 1988, which was accidentally shot down by the USS Vincennes in the Persian Gulf.
Mesbahi, who once reported directly to former Iranian president Akbar Hashemi Rafsanjani and now lives under a witness protection scheme in Germany, told Al Jazeera: "Iran decided to retaliate as soon as possible. The decision was made by the whole system in Iran and confirmed by Ayatollah Khomeni. The target of the Iranian decision-makers was to copy exactly what happened to the Iranian Airbus. Everything exactly the same, minimum 290 people dead."
The documentary claims the Lockerbie bombing was arranged during secret meetings in Malta attended by members of the Iranian, Syrian and Libyan regimes, leaving open the possibility that Libya did play a part in the attack.