The deaths of 270 people killed in the Lockerbie disaster are being commemorated in Britain on the 20th anniversary of the tragedy.The tiny Scottish town became the focus of world attention when a jumbo jet exploded at 31,000 feet sending the plane plummeting to earth, killing all 259 passengers and crew on board. Panam flight 103 smashed into the ground, killing 11 residents as the stricken flight demolished houses, causing a massive crater 10 metres deep. In the aftermath, the finger of blame was pointed at Libya, accused of planting the bomb which brought the plane down. Businessman Abdel Basset al-Megrahi, said to be a Libyan secret service operative, was convicted of the killings. His co-accused was acquitted. But even now, 20 years on, doubt remains about his guilt and the Scottish criminal cases review commission has identified six grounds where it believes there may have been a miscarriage of justice. A second appeal is pending but Megrahi has cancer and may never taste freedom again.