A Maltese shopkeeper whose evidence helped convict Abdelbaset Al-Megrahi of the Lockerbie bombing has died, the BBC has learned.
Tony Gauci died in Malta of natural causes, a retired senior police officer involved the case told the BBC.
Gauci said he had sold Megrahi clothing found wrapped around the bomb which killed 270 people on board flight Pan Am 103, which was blown up in 1988.
Doubts have been raised about his reliability.
Convicted in 2001 before being flown to Scotland to serve his sentence, Megrahi maintained he was innocent until his death in 2012.
The Libyan lost one appeal against the conviction in 2002. Five years later, the Scottish Criminal Cases Review Commission ruled that there were six grounds for a second appeal.
The Commission questioned the evidence regarding the date on which the prosecution said the clothes were bought from Gauci’s shop.
It also said that evidence which cast doubt on Gauci’s identification of Megrahi had not been made available to the defence, a breach of rules designed to ensure a fair trial.
In particular, it said there was evidence that four days before he identified Megrahi, Gauci had seen a photograph of him in a magazine article about the bombing.
There have also been questions raised about money reported to have been paid to Gauci in connection with his participation in the inquiry.
In November 2013 the Crown Office said: “No witness was offered any inducement by the Crown or the Scottish police before and during the trial and there is no evidence that any other law enforcement agency offered such an inducement.”
The retired officer spoke of Gauci’s “great honesty, integrity and bravery in the face of constant threats as a result of the evidence he gave”.
In 2014, Scotland’s top prosecutor, Lord Advocate Frank Mulholland reaffirmed his belief that Megrahi is guilty.
He said no Crown Office investigator or prosecutor had ever raised concerns about the evidence used to convict him.
The Pan Am flight exploded over Lockerbie, in the south of Scotland, on 21 December 1988.
As well as 259 people on board the aircraft, 11 residents of Lockerbie died on the ground as a result of a giant fireball as the plane crashed to the ground.
The Scottish government released Megrahi on compassionate grounds in August 2009 after he was diagnosed with terminal cancer and given six months to live.
He returned to Libya, where he died in May 2012.
Key Lockerbie witness Tony Gauci dies in Malta