EVIDENCE that led to a Libyan being imprisoned for the Lockerbie bombing had been tampered with and overlooked and witnesses not questioned in an attempt to divert the investigation away from the original suspects. The claims form the basis of his appeal which is expected to be given the go-ahead this week.

Hundreds of documents will form the basis of Abdelbaset Mohmed al-Megrahi s defence case which the Scottish Criminal Cases Review Board (SCCRB) could announce will go to a re-trial. If al-Megrahi walks free the Scottish legal system faces huge embarrassment.

The documents cast doubt over key prosecution claims which helped convict al-Megrahi, 54, of the bombing which claimed 270 lives, including the credibility of the Maltese shop-keeper Tony Gauci who sold him clothes which traced back to his store and were found scattered around the Dumfries-shire countryside after the December 1988 atrocity.

A question mark has always hung over Gauci s testimony to al-Megrahi s trail at Kamp Zeist, in the Netherlands, where the showpiece trial was staged seven years ago. However, al-Megrahi s defence papers show their main plank against the crown s case is that Gauci made two earlier statements in which he identified the convicted Egyptian terrorist Abu Talb.

Gauci, who had difficulty identifying al-Megrahi as the man who bought the clothing from subsequent photographs, had given statements claiming that he didn t remember selling the shirts to the man. However, he was able to recollect when questioned six months later selling the shirts and how much they had cost.

His evidence is crucial as the clothing remains contained debris from the bomb which exploded aboard Pan Am Flight 103. He was the only person to directly link al-Megrahi to the bomb.

He never fully confirmed his identification of al-Megrahi as the buyer in an ID parade, photographs and an identity parade. He also gave conflicting statements about the height and age of the man who entered the shop.

The convicted man s defence also found alarmingly that that two of Gauci s statements have gone missing, adding fuel to the conspiracy theories surrounding the downing of the jumbo jet.

In defence documents, two of which were overlooked by the Crown, Gauci identified Talb from a photograph taken from a video in October 1989, which he said was similar.

The defence have also found that, despite extensive trawls of the witness statements, two of Gauci s S4677J and S4677S are missing.

Al-Megrahi s team also found inconsistencies in the evidence surrounding a child s baby-gro, which the prosecution had claimed was wrapped around the Toshiba radio cassette which exploded in mid-air in the hold of the London Heathrow to New York flight.

The charred fragments of the child s clothing were apparently shown to the trial suggesting it was very close to the initial explosion.

However, statements casting doubt on the credibility of the cause of the blast came from two mountain rescuers whose evidence that they found an intact baby-gro was submitted to the SCCRB. The statement read: In the statements noted from these witnesses, they are both adamant that they remembered finding an intact baby-gro.

Other key parts of the defence submission include claims that a radio cassette manual, the trial had heard was found shredded alongside the Toshiba BomBeat radio, was also discovered in one piece. The evidence played a crucial part in al-Megrahi s conviction because it provided the link to a minute piece of the bomb s mechanism which was linked to the Libyan.

A 70-year-old woman from Northumberland had given evidence to the trial that the document was found intact, but police later presented it with charring.

They explained it was crucial evidence because of its closeness to the blast.

Meanwhile, a forensic scientist, Dr Thomas Hayes, who gave evidence to the trial that he had identified the charred remains of the baby-gro in the suitcase which contained the bomb, which from its labels led investigators to Gauci s shop appears to have had a new page added to his records.

The SCCRB were said to have been troubled by the addition of Page 51 to his evidence about the discovery of fragments from a Slalom shirt which had particles of the bomb timer s mechanism.

Al-Megrahi s team claim to have proof from German police files that fragments of the bomb timer were found on the shirt in January 1990. The documents are said to contain photographs showing a piece of the shirt with most of the breast pocket undamaged. However, images of the shirt were presented to the trial in a different state, showing a deep triangle-shaped which continued into the pocket.

The shirt s manufacturers were enlisted by the defence and pointed out the shirt was a boy s size, rather than an adult s by virtue of the fact the breast pocket was 2cm narrower than on the adult-sized shirt. The report to the SCCRB is scathing about this evidence stating it is the culmination of a co-ordinated effort to mislead the court .

The report said: There has been a co-ordinated effort to mislead the court in relation to this item, amounting to a perversion of the course of justice. It will be asserted that the item (the shirt collar) could not have been examined...on 12 May 1989 and that th items of evidence were not extracted from it at the time as claimed by him in his evidence.

The defence is convinced that it was politically important for the prosecution to alter evidence in 1990. With the first gulf war, it was necessary to avoid antagonising Iran, and Libya was the perfect scapegoat.

That meant the investigation was moved from targeting the most prominent suspect, Egyptian Alu Talb and the Palestinian terrorist organisation PFLP-GC.

Talb is currently serving a life sentence in Sweden for bombing a synagogue in Denmark in 1985. He is a former member of the Palestinian Popular Struggle Front (PPSF). Al-Megrahi s defence stated in a special defence lodged before the start of the 2000 trial that both organisations were responsible for the bombing and Talb was called to give evidence. However, he denied responsibility for the bombing and never appeared at Kamp Zeist.

The defence papers claim the main force behind the planted evidence and cover-up were CIA operatives, but it suggests that police and others investigating the disaster were involved in the preparation of evidence.

In addition, a former senior Scottish police officer who was involved in the Lockerbie investigation at the highest level is understood to have made statements to the SCCRB supporting allegations that evidence was planted.

The SCCRB will publish its decision on Thursday. Our Search for the truth

The Sunday Herald has an enviable reputation for pursuing the truth in the case of the bombing of Pan Am 103. Our commitment has not always been comfortable. We have been attacked by our peers, challenged by the Lord Advocate himself from the floor of Camp Zeist during the original trial and threatened with legal action.

Much of the material collated by the Scottish Criminal Cases Review Board has previously been extensively aired in these pages. The fabrication of evidence, the doubts over Maltese shopkeeper Tony Gauci s testimony, the money trail leading back to a Palestinian terror group and the terrorist Abu Talb have all been revealed over the years.

In our editorial on the weekend after al-Megrahi was convicted, we wrote: A Libyan suspect was given a life sentence for the biggest mass murder in British history. But too many doubts remain about the wider picture, too many trails remain unexplored, too many questions have still to be answered.

Those questions remain unanswered and the sense that justice has not only been denied to al- Megrahi but to the families of the 270 victims of the atrocity continues to gnaw. Hopefully the appeal which is expected to be announced on Thursday will have the authority and courage to finally get to truth.