Conspiracy theorists have for years made hay over the mystery of Pan Am Flight 103 and how it came to explode over a small Scottish town four days before Christmas in 1988.

Among the 400 pages of documents submitted by lawyers for Abdul Baset Ali al-Megrahi to the Scottish Criminal Cases Review Commission were claims of evidence tampering, withholding of vital documents and a distortion of the truth to try to “reverse-engineer” the case against the Libyan – in short, to make the evidence fit the proseuction case.

However, in a statement, the commission said yesterday that it had found “no basis for concluding that evidence in the case was fabricated by the police, the Crown, forensic scientists, or any other representatives of official bodies or government agencies”.

Its findings are that the eight-month trial at Camp Zeist in the Netherlands was potentially flawed, not because of a giant conspiracy or cover-up, but because a single human witness was at fault.

Key to the prosecution’s case was the testimony of Tony Gauci, owner of a small shop in Sliema, Malta. It was here, according to the Crown, that clothes were bought that were placed inside the Samsonite suitcase that carried the bomb.

Mr Gauci’s evidence linked the bomb timer directly to Megrahi via an apparently random selection of clothes bought from his shop on a date – December 7, 1988 – when the Libyan was in Malta.

Some 19 of Mr Gauci’s statements were disclosed to the trial, and although they were deeply inconsistent, his evidence was accepted as “reliable” by the three judges.

In two early statements the shopkeeper appeared to identify Mohammed Abu Talb – an Egyptian terrorist who was a member of the Popular Front for the Liberation of Palestine General Command – as the purchaser.At the same time he described the purchaser as 6ft tall and about 50 years old. Megrahi, however, was 5ft 8in and 36. Mr Gauci repeatedly changed his story in statements to police, although he never categorically identified Megrahi, only saying that he “resembled” the man who bought the clothes.

However, the most damning assessment of the shopkeeper’s credibility did not come until four years after Megrahi’s conviction. Speaking in 2005, Lord Fraser of Carmyllie, Scotland’s Lord Advocate at the time of the bombing, described him as “not quite the full shilling” and “an apple short of a picnic”.

In a 14-page summary of its 800-page report, which will not be made public, the SCCRC said it had found six grounds where it believed that “a miscarriage of justice may have occurred and that it is in the interests of justice to refer the matter to the Court of Appeal”.

Although it revealed just three of the six grounds, it said that there was no “reasonable basis” for the court’s conclusion that the clothes were bought from Mr Gauci’s shop on December 7, 1988. It said that new evidence suggested that the clothes were bought some time before December 6.

The SCCRC’s four investigators also raised questions about Mr Gauci’s reliability after discovering that he was found with a photograph of Megrahi four days before an identification parade in April 1999.

It added that “other evidence” in its possession may further undermine Mr Gauci’s testimony, but did not elaborate. However, it is believed that at least some of this evidence may be classified material from intelligence sources.

Mr Gauci’s testimony was crucial in securing Megrahi’s conviction, but the Libyan was also linked to the bomb through a tiny fragment of circuit board, said to have come from the detonator, which was traced to a Swiss electronics manufacturer with whom Megrahi had a known association.

The precise circumstances surrounding the discovery of the fragment – who found it and when – have long been shrouded in mystery. But the SCCRC insisted that the circuit board had not been tampered with or fabricated, as some have suggested. It added that there was no evidence to suggest there had been “unofficial CIA involvement” at the crash site or that items found at the scene had been “spirited away”.

The case, which will go before five Appeal Court judges, will be called for a preliminary hearing at the High Court in Edinburgh within the next six weeks. However, it could be up to two years before the appeal is heard in full.

Tony Kelly, Megrahi’s lawyer, suggested yesterday that he could apply for bail before the end of the year.

The 2001 trial

84 days of evidence over eight months

230 witnesses called

10,232 pages of transcript

621 exhibits

£80m cost, including £12m for a special court, media centre and prison complex at Camp Zeist, near Utrecht, in The Netherlands

Source: Times database

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