The tail section of the TWA 747 is unloaded at the Brooklyn shipyard. (Newsday / Viorel Florescu)

They explode in an instant, leaving behind twisted metal, broken hearts and unanswered questions.

But a bomb that destroys an airplane also leaves behind clues, silent evidence as compelling as a fingerprint on a murder weapon. If a bomb brought down TWA Flight 800, experts say, the bomber's fingerprints are out there, perhaps waiting to be discovered on the ocean floor.

"The entire area around there has to be combed to see if there are any pieces that are missing. You want to find as much stuff as possible," said Daniel Slowick, who runs a firm based in Palmer, Mass., that investigates fires and explosions. "But in the end," he said, "the work facing investigators will be a lot like assembling pieces of a jigsaw puzzle."

In a disaster that bears some resemblance to Flight 800, an Air India plane traveling from Canada to London disappeared from radar off the coast of Ireland in June, 1985, killing all 329 people on board. Wreckage settled to a depth of about 6,700 feet.

Searchers using deep-sea diving vehicles eventually retrieved enough pieces of aircraft for investigators to conclude it had been downed by a bomb. The fuselage in the vicinity of the forward cargo hold been punctured by small holes, the petals of which curled outward until they made circles.

That and other evidence, including damage to the plane's right wing caused by flying debris, "directly points to ... a bomb in the forward cargo hold," the Indian panel that investigated the disaster concluded. Investigators blamed the attack on Sikh extremists.

A bomb also creates a pressure wave that travels outward in all directions. As the wave comes into contact with dust or other small particles, it gives them a high-speed ride, ending in the blink of an eye when the particles become imbedded in a nearby object or person.

When an aircraft fuselage is exposed to a pressure wave fueled by high explosives, its metal surface will develop such pitting, Slowick said. Invisible to the naked eye, the damage is detectable by microscope.

Only a bomb fueled by high explosives can produce a signature like that, experts say. That allows investigators to distinguish between a bomb and, for example, an exploding gas canister. Other clues can be found through chemical analysis, said Frank Fleming, a partner in the Manhattan-based law firm of Kreindler & Kreindler, which represented many of the relatives of the 1988 Pan Am bombing over Lockerbie, Scotland.

"When you look at residues on metal, you might be able to find traces [of a high explosive] ... and say, 'Aha, this has the chemical composition that we only see in dynamite, or plastic explosive, or whatever.' " Fleming said. Metal fragments closer to the source of the explosions will have more tears or bends than those further away. "The investigators will look for this deformation on the metal," Fleming said. From that, "they'll be able to determine where on the plane the explosion took place."

In Lockerbie, it took investigators seven days to announce they had found conclusive evidence of a bomb. Ultimately their painstaking search of 845 square miles of Scottish countryside yielded more than 10,000 items, including a vital clue: a green sliver of circuit board embedded in a shirt packed inside the suitcase that contained the bomb.

The board was part of a bomb timer. Markings on the board led investigators to the Swiss firm that had manufactured it for Libya. The evidence led the United States and Britain to accuse two Libyans of planting the bomb.