It was some group like the PLO, cant recall their exact name. They vowed to down an american airliner in revenge for the 300-odd muslims killed when the US airforce accidentally shot down a civilian plane a year or so earlier. Jim Swire, whose daughter was killed in the Lockerbie attack, dismissed the verdict againt Al Megrahi as ludicrous, and is still looking for justice against the people that did it, and the man who designed the trial system used in the case called the actual trial and verdict "a travesty of justice". Paul Foot wrote a full report on it called "Lockerbie- The flight from justice", probably the most thorough investigation yet.