(Abu Nidal reportedly worked for the CIA and MOSSAD...)
Reportedly, Abu Nidal may have played a part in the Lockerbie Bombing.
Abu Nidal's organisation has worked with the PFLP-GC (Popular Front for the Liberation of Palestine - general Command)
2. Reportedly Ahmed Jibril (founder and leader of the PFLP-GC) had a base near Frankfort.
Reportedly, Jibril had links to alleged drugs dealer al-Kassar, who allegedly was working with the CIA in smuggling drugs into the USA on PanAm flights.
Reportedly the maker of the Lockerbie bomb was Marwan Kreesat (Khreeshat). Bomb maker Marwan Abdel Razzack Khreesat was part of Jibril’s cell.
On 26 October 1988, Khreesat was arrested and one of his bombs seized.
Then Khreesat was mysteriously released. 
Former CIA agent Oswald Le Winter stated, "…pressure had come from Bonn… from the U.S. Embassy in Bonn… to release Khreesat." 
Reportedly, Khreesat worked for U.S. intelligence. 
Allegedly, one of Khreesat's bombs was used to bring down Pan Am flight 103 over Lockerbie.
3. Former UK Labour MP Tam Dalyell and Edinburgh law professor Robert Black have urged the Scottish and UK governments to answer reports that Abu Nidal was a US agent.
"They have long believed Abu Nidal, who died in Iraq in 2002, and his Popular Front for the Liberation of Palestine General Command were responsible for co-ordinating the bomb that blew up Pan Am flight 103 over Lockerbie on 21 December, 1988 with the loss of 270 lives."
Intelligence reports, said to have been drawn up for Saddam Hussein's security services, said Kuwaitis had asked Abu Nidal, to do work for them in Iraq.
"The reports referred to Abu Nidal's 'collusion with both the American and Kuwaiti intelligence apparatuses in co-ordination with Egyptian intelligence'." - (Was Lockerbie suspect working for US? - News)
4. "Lockerbie campaigners have urged the UK Government to press Washington over claims that a now-dead terrorist leader was an American spy.
"Former Labour MP Tam Dalyell and Edinburgh law professor Robert Black said the claims should also be investigated by prosecution authorities in Scotland."
"The claims that Abu Nidal was working for the Americans would explain some of the mysteries that surround the Lockerbie outrage, they said." - Lockerbie campaigners seek answers
5. "THE CHIEF architect of the trial which convicted Abdelbaset Ali Mohmed al-Megrahi of the Lockerbie bombing has accused two of Scotland's most senior legal figures of treating the Libyan "shabbily" by delaying his appeal...
"Robert Black, professor emeritus in Scottish law at Edinburgh University, said that Lord Advocate Elish Angiolini and the Advocate General for Scotland, Neil Davidson, were responsible for delays in the appeal process." - Lockerbie bomber treated ‘shabbily’ says professor