By Roger Hardy
BBC Middle East analyst
The legal review of the case of Abdelbaset al-Megrahi has re-opened the Lockerbie affair in a dramatic fashion.
In all 270 people died in the bombing over Lockerbie
It raises a host of awkward questions.
Was the original trial of the former Libyan intelligence agent fatally flawed, as his lawyers maintain?
Was the evidence contaminated by the American or British authorities?
Was Libya implicated out of political expediency, when all along the main suspect was Iran?
Pan-Am 103 exploded over the little town of Lockerbie in Scotland on 21 December 1988, killing a total of 270 people.
The initial suspicion was that Iran had exacted revenge for the shooting-down of an Iranian civil airliner over the Gulf a few months before.
A US warship had mistakenly believed it was under attack from the plane, when in fact it contained pilgrims on their way to Mecca.
Iran offered a $10m reward to anyone who avenged the attack.
It looked as if the offer had been taken up by a radical Palestinian group, the Popular Front for the Liberation of Palestine-General Command.
The Syrian-based PFLP-GC was led by Ahmed Jibril, who had close links with both the Syrian and Iranian regimes.
But despite these early suspicions, the focus of the investigation abruptly switched to Libya - and Megrahi was eventually convicted in 2001 at a special court in the Netherlands.
Some believed - and still believe - this sudden switch was the result, not of convincing new forensic evidence, but of political expediency.
Abdelbaset Ali Mohmed al-Megrahi has always insisted he is innocent
After Saddam Hussein's Iraq invaded Kuwait in 1990, the West needed the support of Syria and Iran.
To get those two countries off the hook - so the argument ran - Libya was made the scapegoat.
Mr Megrahi's first appeal, in 2002, was rejected. But now a Scottish review board has said the case must be re-examined.
The fallout will be significant.
Even before the board's ruling, Jim Swire, whose daughter died in the bombing, expressed his deep frustration to the Scotsman newspaper.
"Scottish justice obviously played a leading part in one of the most disgraceful miscarriages of justice in history," he said.
"The Americans played their role in the investigation and influenced the prosecution."
Megrahi and the Libyan government will be quick to claim that he is innocent, as they have claimed all along.
He may seek to sue either the Scottish or the British authorities for wrongful conviction.
Libya could demand the return of the $2.7bn in compensation it paid to the victims' families - without ever accepting guilt.
Because of the magnitude of the case, there will be considerable embarrassment in both Washington and London.
Will we ever know who was behind the Lockerbie bombing?
Oliver Miles, former British ambassador to Libya, has his doubts.
"No court is likely get to the truth, now that various intelligence agencies have had the opportunity to corrupt the evidence," he told the BBC.
The review board, however, insisted it had "found no basis for concluding that evidence in the case was fabricated by the police, the Crown, forensic scientists, or any other representatives of official bodies or government agencies".
Almost two decades on, the Lockerbie puzzle has come back to haunt those originally tasked with solving it.