ABU TALB emerged soon after the Lockerbie bombing as a key suspect in the atrocity. Talb, an Egyptian, belonged to a splinter group of the Popular Front for the Liberation of Palestine - General Command (PFLP-GC).
Shortly after the focus of the inquiry switched to Libya, Talb demonstrated his murderous talents with a bomb attack on a Danish airline office that left one dead. Jailed for life, he caused enormous controversy by appearing at the Lockerbie trial as a prosecution witness, earning lifetime immunity in return.
But defence documents sent to the commission, and seen by Scotland on Sunday, once again support the theory that it was Talb and his associates, not Megrahi, who blew Flight 103 out of the sky.
New information about Talb and his activities in Europe has been presented to Megrahi's defence team by Robert Baer, a retired CIA agent, who has provided evidence and made statements that are now before the Scottish Criminal Cases Review Commission.
Baer's evidence, based on sightings of top-level intelligence information and backed up by documentary records he has seen, indicates Iran was behind the bombing and paid the PFLP-GC to carry it out.
The report to the commission says: "Both Talb and the PFLP-GC received substantial payments after the bombing - [Baer] has details of the bank accounts: $11m to the PFLP-GC in Lausanne on 23.12.88 [two days after the bombing]; $500,000 to Talb 25.4.89 in Frankfurt. Both Talb and [Hafez] Dalkamoni [leader of the PFLP-GC cell in Germany] appeared in the Iranian Role [sic] of Honour in 1990 for great service to the Iranian Revolution."
Baer, who was directly involved in the Lockerbie investigation until 1991, has assured the defence team that the payments were made by the Iranian government.
Baer had previously offered to meet the defence team leading Megrahi's first appeal, the same lawyers who represented him at his trial, but his offer was rejected and the new evidence he was offering was not raised at that time.
Baer has been able to give a unique insight into the internal views and discussions of senior US investigators on Lockerbie. He has made it clear to the defence team that even after the focus shifted in public to Libya, agents remained convinced of involvement by the PFLP-GC and Talb.
Baer says the $11m paid to the PFLP-GC in Lausanne, Switzerland, was transferred to another account held by the terrorists at the Banque Nationale de Paris and was later moved to the Hungarian Trade Development Bank.
Baer has also revealed the CIA had intelligence from totally reliable sources that Talb and Dalkamoni were Iranian agents who earned their places on the government roll of honour for their services to the "Islamic revolutionary struggle against the west".
The defence also has evidence that American agencies regarded Talb and his associates as the real bombers, long after a warrant was issued for Megrahi's arrest in 1991.
Confidential documents from the US Defence Intelligence Agency, dated January 1993, were still describing the PFLP-GC as the Lockerbie bombers. What the agency discussed in private was very different from what it was telling the world. It has also emerged that, as recently as 2002, a year after Megrahi was convicted and just a few weeks before his appeal was dismissed, CIA internal documents named Talb as the bomber.
It's well known the very first suspects in the days after the bombing were members of the PFLP- GC, led from Damascus by a former army officer, Ahmed Jibril, and funded by Iran.
Jibril's right-hand man, Dalkamoni, was a frequent visitor to Europe. In 1988, Dalkamoni had a cell operating in Germany. Among them was the group's master bomb-maker, Marwan Khreesat.
According to the theory, Talb was dealing with the cell from his base in Sweden and travelled to Frankfurt on more than one occasion, as well as visiting Malta where he may have bought clothes from shopkeeper Tony Gauci that were later found amid the Lockerbie wreckage.
In October, an intelligence operation codenamed Autumn Leaves led the German secret police to raid the flat in Neuss where Khreesat was making his bombs, concealed within Toshiba radio-cassette recorders. Four devices were recovered, but Khreesat, a Jordanian, revealed later that a fifth device had been taken away by Dalkamoni before the raid and was never recovered. It is believed Dalkamoni passed the bomb to Talb, who had the airline contacts that allowed him to get it on to Flight 103.
Iran had instructed the group to avenge the deaths of 290 people caused when an American vessel shot down an Iranian Airbus over the Gulf six months before Lockerbie.
Khreesat revealed in a remarkable interview with John F Kennedy's former press spokesman, Pierre Salinger, that he always believed it was his bomb that had been used to bring down Pan Am 103.
His bombs were operated by a barometric pressure device that triggered a simple timer with a range up to 45 minutes. Each of the devices recovered in the raid were set to run for about 30 minutes after being triggered. On a jumbo jet, the pressure change would have occurred seven minutes into the flight and an explosion would have followed some 30 minutes later.
Pan Am 103 blew up 38 minutes into its flight. Yet if the explosion had been triggered by the sophisticated MeBo timer, the device would have had a range of 99 hours. Any bomber who wanted to get away with the crime would surely have triggered the explosion at a time when the plane was bound to be over the Atlantic Ocean.
The bombing was carried out by the CIA and the Defence Intelligence Agency (DIA) to cover up a drug-trafficking network they had created to fund the release of six US hostages held in the Lebanon.
The plan is said to have been organised with the help of the Israeli intelligence agency, Mossad, which used its contacts in Hezbollah, the pro-Palestinian group behind the Americans' kidnapping, to arrange heroin shipments.
The narcotics, paid for by the White House, would be shipped out of Lebanon on Pan Am flights by couriers into America, and the money subsequently gleaned from its sale was then used to pay the kidnappers' ransom demands.
But during one of these 'runs', one of the bags containing the drugs was swapped for one containing a bomb, planted by a group on behalf of the Iranian government, which wanted revenge for the downing of an Iran Air jet in 1988.
• It has been alleged the US government allowed the bomb plot to go ahead, because on board was Major Charles McKee, a US intelligence expert who had discovered the drug-trafficking scam.
• The US government had been tipped off about an attack prior to Flight 103 happening. Some claim a secret memo, passed to American embassy staff, warned of a threat to bomb a Pan Am flight returning to the US 10 days before Lockerbie.
This led a number of senior US personnel to change their travel plans and switch from Pan Am 103 to other flights.
• Rescue volunteers discovered a large red tarpaulin on the ground shortly after the crash, but when they approached, armed men in a US helicopter warned them off. Likewise, local farmer Innes Graham was reportedly told by American-sounding individuals to stay away from a copse on the outskirts of Lockerbie.
• Two coachloads of American investigators arrived at the scene the day after the crash and among their luggage was a single coffin. Labour MP Tam Dalyell later alleged they had stolen a body. A local doctor is said to have labelled and tagged 59 corpses only to return the following day to find the US authorities had re-tagged all of them, but now there were only 58 bodies.
• Some say there was not even a bomb, and the explosion was by an electrical fault or decompression.