Scotland's High Court began hearing an appeal on Tuesday against the conviction of a Libyan man found guilty of the 1988 Lockerbie aircraft bombing, the deadliest militant attack in British history.
Pam Am Flight 103 was blown up over the Scottish town of Lockerbie in December 1988 en route from London to New York, an attack that killed 270 people, mostly Americans on their way home for Christmas.
In 2001, Libyan intelligence officer Abdel Basset al-Megrahi was jailed for life after being found guilty of the murder of 243 passengers, 16 crew and 11 residents of Lockerbie who were killed in the attack. He is the only person to be convicted over the bombing.
Megrahi, who denied involvement, died in Libya in 2012 after being released three years earlier by the Scottish government on compassionate grounds following a diagnosis of terminal cancer. His family have made a posthumous appeal against his conviction.
Their lawyer, Claire Mitchell, began by arguing that the evidence presented by the prosecution in the original trial was flawed to the extent that the case against Megrahi was not proven.
"No reasonable jury, properly directed, could have reached a guilty verdict" based on the evidence, she said.
She said that the prosecution case rested on evidence that the suitcase carrying the bomb contained clothing which it said was traceable to Megrahi, but the absence of any explanation as to how the case got onto the Pan Am flight was a critical issue.
In 2003, then-Libyan leader Muammar Gaddafi accepted his country's responsibility for the bombing and paid compensation to the victims' families, but did not admit personally ordering the attack. However, Megrahi's family and some relatives of the Scottish victims have always doubted his guilt.
In March, an independent Scottish review body ruled Megrahi's family could launch an appeal after concluding there might have been a miscarriage of justice.
"Overturning of the verdict for the Megrahi family and many of the families of British victims also supporting the appeal, would vindicate their belief that the governments of the United States and the United Kingdom stand accused of having lived a monumental lie for 31 years," the family's lawyer, Aamer Anwar, said in a statement ahead of the hearing.
Megrahi first appealed in 2002 but this was refused by Scotland's High Court. A second appeal was abandoned in 2009 just before his return to Libya.
