The theories: More than 90% of the wreckage was recovered and initially a criminal investigation was launched by the FBI.
Four years later an official report concluded that the crash was probably caused by an electrical short circuit that set fi re to vapour in a fuel tank causing an explosion.
But sceptics insist there has been a cover-up and say that the real cause was a missile strike either from a terrorist or mistakenly fi red by a US Navy vessel.
Others suggest that there was a bomb on board the plane. Last year a TV documentary claimed to have evidence from radar data that backed up the notion of an explosion caused by an external source.
There are also claims that suspicious explosive residue was found amid the wreckage.
Some investigators who worked on the original crash have now called for the case to be re-opened.