The force required to embed the material in the cargo container wall was clearly far in excess of that which could be produced by anything other than a bomb explosion. A piece of the cargo container in which the bomb had been planted was embedded with parts of the radio-cassette player. Since then, the X-raying of bodies or body-fragments has become standard procedure in cases where bombs are suspected.There are other characteristics of bomb explosions, among them the feature that first alerted investigators to the likelihood of a bomb having downed PanAm 103 over Lockerbie in 1988. Newton and his team positioned rods and wires along the trajectory on which the objects had entered the bodies and the cushions and were able to work out where the bomb must have been placed. Similar fragments were found in the seat cushions.This provided not just evidence, but positive proof that a bomb had exploded on the plane. One of the indecencies of such tragedies is that, for the purposes of a crash investigation, human remains are as much forensic evidence as the other items of wreckage. The victims may, for instance, display signs of eardrum damage or overpressure on the lungs which will point to particular types of explosion.In 1967, for example, a British Comet airliner plunged into the Mediterranean, leaving only a few bodies and seat cushions on the surface, with the main wreckage too deep to recover.

The then chief investigating officer of the UK's Accident Investigation Branch, Eric Newton, asked the pathologists to X-ray the bodies. Tiny fragments of metal were found in some of them which could only have entered the bodies at a velocity far higher than any impact force, or from the force of a fuel explosion. If some kind of mechanical cataclysm did occur, all sorts of clues could present themselves. Investigators can, for example, examine the filaments in the bulbs of individual warning lights. If any were alight at the moment of the tragedy, the filaments will have been elongated slightly and will remain frozen in that state today.THE bodies of the victims can reveal crucial evidence. There will also be chemical residues of the explosive and its detonator. If a missile was involved, the investigators will find inward-pointing jagged edges on the remains of the part of the plane nearest the detonation or where the missile struck.Still more arcane is the work that can be done inside the cockpit once it is located.

High explosive detonates at a vastly greater rate than a fuel explosion, between 1,000 and 8,000 metres per second, much faster even than the high-speed debris of a disintegrating jet engine.Under the microscope a bomb-damaged piece of aluminium or titanium, for example, will betray the velocity of the explosion and show hot-gas erosion, where the surface of the metal is seared by the extreme heat. Under an electron microscope there are a wide variety of features, such as pitting, curling, or fusing of the metal that are characteristic only of bombs. Explosions, fires, bombs and in-flight break-ups of planes all have characteristic signatures. An aviation-fuel vapour explosion will leave residues on the surfaces, and the forces that such explosions can exert have been quantified.