A documentary to be broadcast on Al Jazeera claims that new evidence shows the Lockerbie bombing was ordered by Iran and carried out by Palestinians.
A former Iranian intelligence officer says the 1988 bombing was ordered by Iran, not Libya, as is commonly believed.
The man, who has defected to Germany, says in the documentary that the attack was in retaliation for a US navy strike on an Iranian commercial jet earlier that year. At the time, the USS Vincennes said it believed it was under attack and blew up the plane as an act of defence.
Libyan Abdelbaset al-Megrahi is the only person to have been convicted of the bombing of Pan Am flight 103 on 21 December 1988, which blew up over the Scottish town of Lockerbie. All 243 passengers and 16 crew - most of the American - died, and a further 11 people were killed in their homes when wreckage hit the groun.
Al-Megrahi was released from jail by the Scottish government on compassionate grounds after being diagnosed with prostate cancer, and died last year protesting his innocence.
On the 25th anniversary of the bombing last december, the British, American and Libyan governments vowed to work together to reveal the full facts of the bombing. They said they wanted "all those responsible for this most brutal act of terrorism brought to justice".