Twenty-five years after the Lockerbie bombing, Al Jazeera has uncovered evidence which casts doubt over the entire investigation and trial into what was the biggest case of mass murder ever seen in Scotland.
Documents obtained by the network, and verified by security and legal experts, point to the involvement of Iran's secret service, Hezbollah and the armed group The Popular Front for the Liberation of Palestine (PFLP) - General Command.
The investigation found that the PFLP was responding to requests from Iran to avenge the shooting down of Iran Air Flight 655 by the USS Vincennes in July 1988, which killed 290 people.
Classified US Defence Intelligence Agency cables obtained by Al Jazeera say: "The execution of the operation was contracted to Ahmad Jabril, Popular Front for the Liberation of Palestine General Command (PLFLP-GC) leader. Money was given to Jabril upfront in Damascus for initial expense. The mission was to blow up a Pam-Am flight."
Al Jazeera's investigation found a meeting took place between the parties in Malta nine months before the bombing of the Pan Am flight, with the purpose of the meeting to discuss potential US and Israeli targets to attack and, or, blow up.
The Al Jazeera investigation also gains access to the confidential Bird Report, which was commissioned by Abdelbaset Al-Megrahi, the Libyan convicted of the bombing, before he dropped his appeal.
Al Jazeera also interviewed a senior Iranian intelligence official and a former CIA agent.
"Six days after taking down the Airbus there was a meeting in Beirut, we know where it occurred. The Iranians went to the PFLP-GC, the break off faction and said, alright you guys know how to bring down airplanes, bring down five, five civilian airliners," former CIA agent Robert Baer said.
Criticising the subsequent path taken by the investigation and resultant trial, Baer said his opinion was not a controversial one among those involved.
"The CIA and the FBI investigations diverged completely… because the case was, being run by the Department of Justice, in complete disregard to the intelligence. As far as I can tell is someone said, look, Libya's vulnerable to prosecution, small country, Gaddafi's hated, let's go for it.
"It was an executive decision, and then once that happened everybody lined up. So the people in the intelligence community could just go bugger off you know. Yeah fine, take your theories and run off. And that works until the evidence is proved, you know, to be faulty.
"I'm not giving you a controversial opinion here. I kept up with all of the CIA, intelligence side, and to a man they’ve said it was Iran."
Al Jazeera tracked down two of the PFLP-GC members to whom the evidence points.
Abu Talb now lives in Sweden, while bomb-maker Marwan Khreesat lives in Jordan. A source close to him confirmed to Al Jazeera that the attack had been commissioned by Iran, and that the bomb was put on board the plane at London's Heathrow airport.
The documentary is Al Jazeera’s third in-depth investigation into the Lockerbie atrocity. The previous films gained exclusive access to the Scottish Criminal Cases Review Commission report and raised serious questions about the safety of Megrahi’s conviction.
Al Jazeera's Jamal Elshayyal reports.
Lockerbie: What Really Happened? will air on Tuesday 11 March at 2000GMT on Al Jazeera English.