Among the grounds for doubt was new evidence indicating al Megrahi may not have been in Malta when the clothing was purchased. It was also revealed that four days before the ID parade at which the Maltese store worker picked out al Megrahi, he had seen a photograph of the Libyan in a magazine article linking him to the bombing.
Al Megrahi insisted on his innocence right up to his death. Some of his supporters claim he may have been a convenient scapegoat.
Libya's leader Muammar Gaddafi was a longstanding supporter of terrorism around the world, but by the late 1990s wanted to end his country's pariah status.
After lengthy negotiations, Libya accepted responsibility for "the actions of its officials" over Lockerbie, agreed to pay more than $2 billion in compensation to victims' relatives, and surrendered Megrahi to the Scottish authorities for trial.
Libya gave up its weapons of mass destruction, and shared intelligence with the United States on al Qaeda in the region. In turn, Western governments and companies were keen to exploit the country's important oil and commercial potential.
After Gaddafi's regime was overthrown, it was hoped that new information may come to light about what led to PA103's catastrophic damage at 31,000 feet above Scotland.
Secretary of State Hillary Clinton said recently that the United States will continue to pursue justice on behalf of the victims.
"The United States has kept open the case concerning the Lockerbie bombing," she said. "We want more information, and we want to have access to those who might have been somehow involved in the planning or execution of the bombing."
Last year Scotland's most senior law officer said he would continue his efforts to investigate the case.
Lord Advocate Frank Mulholland said the idea that Megrahi acted alone was "risible," and added that he would be "failing in his duty" if he did not find the people who were responsible for the bombing.