Two new TV documentaries have raised fresh doubts about the reliability of evidence used to convict Abdelbaset al-Megrahi, the only person convicted of the Lockerbie bombing.
BBC Scotland Investigates and Al Jazeera's Lockerbie: Case Closed claim that new evidence about the bomb timer found after the explosion has cast doubts on the case against Megrahi.
Both programmes examine a report by the Scottish Criminal Cases Review Commission into Megrahi's conviction - a document that was never made public.
The documentaries also question evidence given by Tony Gauci, a Maltese shopkeeper who was one of the prosecution's key witnesses.
On 21 December 21 1988 270 people died when Pan Am Flight 103 exploded over the town of Lockerbie.
Megrahi, who maintains he is innocent, was convicted in 2001 of carrying out the bombing and sentenced to life imprisonment. He was released on compassionate grounds in 2009 after he was diagnosed with terminal cancer and doctors estimated he only had three months to live.
He now lives in Libya.
Scientific analysis in the unpublicised report suggested there were differences in metal coatings used in a fragment of a timer found in the remains of a shirt supposedly bought by Megrahi from Gauci's shop and a control sample from the timer type supplied to the Libyan intelligence.
The discrepancy undermines allegations that Megrahi was working for Libyan intelligence.
Megrahi denied Gauci's claims he had bought clothes from him and had never met thye witness before the 2001 court case.
In his testimony the shopkeeper also said Megrahi had bought an umbrella when he visited the shop on 7 December because it was raining but Maltese meteorologist Joseph Mifsud said it did not rain on the day.
While Gauci claimed that Christmas lights had not yet been put up when Megrahi visited, Michael Refalo, a former tourism minister said he had turned on the lights on December 6.
The Al Jazeera documentary also raised question about Gauci's description of the man he later identified as Megrahi and both reportages said Gauchi had seen a photograph of Megrahi linking him to the bombing in a magazine, before he identified him.