In late December 1988 a terrorist bomb destroyed Pan Am Flight 103 over the Scottish town of Lockerbie and killed 270 people.
Only one man, Abdel Basset al-Megrahi, a Libyan citizen, was tried and found guilty of causing the explosion. But he protested his innocence at the time of his trial in Camp Zeist in Holland in May 2000, and continued to do so up until his death in Tripoli in May 2012.
For three years filmmakers working for Al Jazeera have been investigating the prosecution of al-Megrahi.
|Probe identifies suspects over Lockerbie bombing
Two award-winning documentaries, screened on Al Jazeera in 2011 and 2012, demonstrated that the case against him was deeply flawed and argued that a serious miscarriage of justice may have taken place.
In the first episode, Lockerbie: The Pan Am bomber, we followed defence investigator George Thomson as he revealed how forensic evidence presented at al-Megrahi's trial was not only inaccurate but appears to have been deliberately tampered with.
Then in Lockerbie: Case Closed, we revealed the hitherto secret assessment of the Scottish Criminal Case Review Commission (SCCRC) - an independent public body in Scotland - which had re-examined the case in detail and had recommended that it be referred back to the courts for possible dismissal.
Crucially, our film also showed how new scientific tests comprehensively undermined the validity of the most significant piece of evidence linking the bombing to al-Megrahi and Libya - a fragment of electronic timer found embedded in the shredded remains of a shirt, supposedly bought by the convicted man in Malta.
The timer, the prosecution had claimed, was identical to ones sold to Libyan intelligence by a Swiss manufacturer. But as our investigation proved, it was not identical - a fact that must have been known to British government scientists all along.
Now, in our third and most disturbing investigation, we answer the question left hanging at the end of our last programme: if al-Megrahi was not guilty of the Lockerbie bombing, then who was?
Lockerbie: What Really Happened? will air on Monday, March 17 at 0100GMT on Al Jazeera English.