The two Libyans facing trial for the 1988 bombing of a Pan American airliner over Lockerbie, Scotland, are charged with the murder of 270 people in an alleged conspiracy traced back to 1985.

Scottish prosecutors at a special court set up on neutral territory at Camp Zeist, a former air base in the Netherlands, are seeking to prove that Abdel Basset al-Megrahi and Al-Amin Khalifa Fahima were part of a Libyan plot with unnamed others. 

The accused face three alternative charges — conspiracy to murder, murder, or contravention of the 1982 Aviation Security act. They can only be convicted of one charge. 

Conspiracy to Murder: They are alleged to have conspired with others to destroy a civil passenger aircraft and murder its occupants to further the purposes of the Libyan Intelligence Services by criminal means. The charge includes 11 Lockerbie residents killed when the jumbo jet crashed on the town. 

Murder: This charge refers to the completed crime, not merely the agreement in conspiracy to commit it, and would require a higher degree of evidence. Prosecutors must show a physical link between the accused and the explosion and prove that they actually caused the death of the victims. 

Contravention of 1982 Aviation Security Act: The charge means intentionally destroying an aircraft in service or damaging it so badly that it cannot fly or is no longer safe in flight, or to commit an act of violence on board an aircraft likely to endanger its safety. 

Maximum Sentences: A life sentence is mandatory if convicted of murder or violation of the aviation act. In case of a conspiracy conviction, punishment is at the court's discretion. 

Possible Verdicts: Guilty, not guilty, not proven. In either of the latter two cases, the defendants are acquitted. 

Burden of Proof: The defense does not need have to prove anything to secure an acquittal, merely to raise a doubt as to the prosecution's assertion of the defendants' guilt. 

Corroboration: Each incriminating fact must be supported by two pieces of evidence or credible witness testimonies. 

Appeals: An appeal may be made on the basis of a procedural error, insufficient evidence or wrongful submission of evidence. In case of appeal, the five-judge Scottish High Court in Edinburgh would come to Camp Zeist to hear it. 

The Prosecution's Case: The accused are alleged to have been members of ther Libyan Intelligence Services who used false identities and passports and established a fake tour business as cover for obtaining 20 electronic bomb timers in Switzerland in 1985. 

Occupying managerial positions with Libyan Arab Airlines in Malta, they then allegedly obtained airline luggage tags unlawfully, and ultimately placed a Semtex bomb in a suitcase stuffed with clothes from a shop called Mary's House in Malta. The bomb was built into a radio-cassette recorder and programmed to detonate aboard the Pan Am flight after it left London's Heathrow Airport for New York. 

It was allegedly placed on Air Malta flight PM03a to Frankfurt, Germany, for relaying by Pan Am to New York. 

The indictment details trips, addresses, hotels and events in Libya, East Germany, Switzerland, Senegal, Czechoslovakia and Malta. It alleges that the bomb timers, from a Swiss firm called MEBO, were tested at a special forces training area at Sabha in the Libyan desert. 

Beyond alleging that the bombing was intended to "further the purposes of the Libyan Intelligence Services," the indictment makes no reference to a precise motive for directing the attack at Pam Am Flight 103.