A certain twist in a chunk of fuselage. Burns on flesh and cabin surfaces. The residue of plastic explosives that gathers on debris.
These are the telltale signs that forensic scientists will look for as they try to determine whether a bomb tore TWA Flight 800 out of the sky.
They will search through wreckage and mutilated human remains, looking for the type of evidence that can survive even fire and saltwater.
But unlike a Sherlock Holmes mystery, no one vital clue is likely to give the culprit away. Instead, crash investigators will have to reassemble, almost literally, all pieces of the aircraft they manage to recover - from screws and wires to giant sections of wing.
Beyond the Boeing 747 itself, they will be piecing together luggage, clothing, cockpit and cabin furnishings and, if there was one, the bomb.
Chemical analysis of microscopic samples will be vital. Bombs essentially spray themselves all over the place, their components first turning into gas, then flying outward to encounter relatively cold surfaces, such as metal panels and upholstery. The gas rapidly condenses, like water vapor on a cold windowpane, and turns solid, with some molecules adhering to metal, cloth, even flesh.
Bombs also shoot debris through a plane, leaving a distinctive pattern of small holes with metal edges splayed outward. The pattern is very different from the damage caused by mechanical failure, such as an engine falling off, which would typically slash wide gashes in the fuselage.
“It won’t look the same,” James Crippen, an arson and explosives expert with the Colorado Bureau of Investigation, said of structural failures. “You’ll get a big gaping hole.”
Bombs also typically shoot unexploded chunks into soft materials, such as luggage, seatbacks and cabin partitions, said Michael L. Barr, director of aviation safety programs at the University of Southern California.
National Transportation Safety Board officials spent Thursday fishing debris from the waters off Long Island, a grim collection that included seats, fabric panels, a sizeable section of one wing and scores of charred bodies and floating limbs.
They predicted it would take days or weeks to determine whether a bomb brought down the plane.
“There are people who can look at pieces of metal or cloth and tell if there was an explosion,” said NTSB Vice Chairman Robert Francis.
In 1988, it took investigators a full week to determine that a terrorist bomb had blown up Pan Am Flight 103 over Lockerbie, Scotland, four days before Christmas. The telltale clue was found in samples scraped from the lining of the baggage compartment, which tested positive for plastic explosives. Later, investigators even found fragments of the radiocassette player in which the explosives were stashed.
From the basic facts that are available, many experts say a bomb was the most likely explanation for Wednesday’s crash. Flight 800 went down without warning about 40 minutes after takeoff, about 20 miles off Long Island’s southern shore.
“Airplanes don’t blow up just like that,” Barr said. “I’ve followed 747s since 1970, and I’ve never seen one blow up like that.”