IT all comes back to Tony Gauci. The eyewitness evidence of a Maltese shopkeeper may seem like the unlikely lynchpin of an international terrorism trial, but Abdelbaset Al-Megrahi could not have been convicted of the Lockerbie bombing without it.

Last week, the Scottish Criminal Cases Review Commission decided to refer Megrahi’s conviction back to the Appeal Court for a second time, determining that his conviction on 270 counts of homicide in 2001 may amount to a miscarriage of justice and the interests of justice demand its reappraisal. This is a decision which may have dramatic ramifications for the Scottish criminal justice system and its international reputation.

“Guilty.” Most criminal trials end in just one word. Juries don’t explain how they’ve reached their verdict. They don’t lay out what evidence they accept and what evidence they reject, which witnesses they find credible and reliable and which they conclude were telling tales. Juries don’t give reasons for their decisions.

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But the Lockerbie case was different. More than 82 pages and 90 paragraphs, Lords Coulsfield, Sutherland and Maclean set out their reasons for convicting Al-Megrahi and acquitting his co-accused. And it is those reasons the SCCRC has thrown doubt on this week. There is only one ground of appeal against criminal convictions in Scotland, and that is that there has been a miscarriage of justice.

The SCCRC has two key concerns. The first is that no reasonable tribunal could have convicted Megrahi of the bombing on the evidence heard in Zeist. The second is that the Crown failed to disclose critical evidence about which the defence could have used to throw doubt on Tony Gauci’s credibility and reliability.

To understand why the commission has taken this stance, we’ve got to look into a shopfront in Sliema on the north-east coast of Malta, more than 1570 miles away from the small Scottish town where Pam Am Flight 103 fell from the sky on the December 21, 1988, killing its 243 passengers, 16 crew, and 11 locals on the ground below.

Tony and Paul Gauci owned a clothes shop called Mary’s House. Amongst the reek of burnt jet fuel, human bodies, scattered luggage, and the broken carapace of the disintegrated airliner, investigators found fragments of clothing which had been damaged when the Boeing 747’s hull was breached mid-air.

Some manufacturers’ labels remained legible. Convicting Megrahi in 2001, the trial court in Zeist determined the plane’s fuselage had been punctured by a bomb concealed a brown Samsonite suitcase which had been stowed in the plane’s hull. The trial court also accepted that this suitcase contained 12 items of clothing and an umbrella before the blast. The Crown’s logic was simple. Establish who owned that suitcase and those clothes, and you can establish who was responsible for orchestrating this appalling tragedy.

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Investigators followed the labels to Malta. This led them to the door of Mary’s House, and there they found Tony Gauci. Gauci told them that a Libyan man who resembled Megrahi had purchased clothing of the same brands from him on one of two dates in late November or early December 1988. “He described these items, which included two pairs of Yorkie trousers and various other items which corresponded to fragments found at the crash site.”

This happened, he said, on either December 7 November 28 1988. Gauci was able to isolate the dates because his brother Paul wasn’t manning the shop, but was watching one or other leg of a football match on the telly. Keep these two dates in your head. They are critical. Gauci explained he remembered the Libyan because he had seemed curiously indifferent to the clothes he had been buying. That, and the fact he’d returned to his shop for an umbrella and left for a taxi in the rain.

The significance of this evidence for Megrahi’s prosecution could not have be more profound. If Megrahi could be identified as the purchaser of those clothes, he could be identified as the Lockerbie bomber. The case against him seemed to grow stronger when it was established that Megrahi had been on the island of Malta on December 7 1988, staying in a Holiday Inn nearby. But there was a potential snag: Megrahi wasn’t in Malta on November 28. To convict Megrahi of the Lockerbie bombing, the court had to accept that he was the purchaser of these clothes, and that he had bought them on December 7.

Tony Gauci’s eyewitness identification of Megrahi was always less than definitive. From the outset, his recollection of the purchaser was shot through with inaccuracies. He claimed the purchaser was between 45 and 50 years of age, and at least six feet tall. At the time, Megrahi was just 36 years old, and just 5’8 in height.

The damp weather was intrinsic to Gauci’s story of how he came to recall this particular purchaser of the clothes found on the ground in Lockerbie. And while the meteorological evidence confirmed there had been showers over Sliema during the late afternoon of the November 28 – when Megrahi wasn’t in Malta – only droplets fell on December 7, this wouldn’t have been enough “to wet the pavement.”

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So which date did the trial court conclude was the date of purchase? The rainy day when Megrahi wasn’t on the island of Malta, or the substantially dry afternoon of December 7 when Megrahi was in a hotel nearby? Coulsfield, Maclean and Sutherland decided it must have been the seventh, and Megrahi must have been the purchaser. As the commission concluded last week, this finding “was integral to its ultimate conclusion that he was guilty of the murders libelled”.

Knock this eyewitness identification out, and you break the chain of evidence directly connecting Megrahi to the explosion. Last week, the commission concluded that “no reasonable trial court could have accepted that Mr Megrahi was identified as the purchaser”. I find it difficult to disagree with them.

Disclosure is the second key issue which has been returned to the Appeal Court. Back in 2007, the commission uncovered a memo taken by an investigating officer in 1991 confirmed that Tony Gauci “expressed an interest in receiving money”.

It would appear that he is aware of the US reward monies which have been reported in the press.” This police documentation also showed that Paul Gauci had also expressed a “clear desire to gain financial benefit” from his involvement in the Lockerbie case, and harped on that string persistently in his discussions with police officers involved in the case.

Having tendered their evidence to the court, both men went on to benefit from the largesse of the American Department of State. Under the Rewards for Justice scheme, the SCCRC established that Tony Gauci received $2m for his evidence, with $1m for his brother Paul.

These payments were disclosed to the defence during the Zeist trial.

There was also another significant gap in disclosure. Before participating in an identity parade, the SCCRC has uncovered evidence that Gauci had been presented with photographs of Megrahi. The defence had no knowledge of this either.

It all comes back, in the end, to Tony Gauci.

Over 30 years on from the fall of Pam Am 103, almost two decades after Abdulbaset Al-Megrahi’s conviction, eight years after his death – the lingering doubts about the Lockerbie case remain.

Tony Gauci died in 2016, as have all three of the judges who accepted his testimony and convicted Megrahi in 2001.

The eyes of the world are understandably elsewhere this week, but make no mistake – the new Lockerbie appeal is a case of global significance, with huge potential to embarrass the Scottish criminal justice system and generate a transatlantic political storm.