While walking along the beach near the Shinnecock Inlet, Ed O'Connell saw a square board sticking up in the sand. He pushed it over with his foot.
"When I saw it, I immediately knew what it was," says the history teacher from New Rochelle who summers in Hampton Bays. Just below the sand line was a tag that said, "Life Vest Under Seat."
With that push of his foot, Mr. O'Connell became part of the massive investigation into the cause of last week's downing of TWA Flight 800. It is a clue-hunt that is part forensic science, part tenacity, and part serendipity. It entails methods as straightforward as the collection of bits of debris and as tedious as listening to weeks of the government's electronic eavesdropping tapes.
With the world media peering over their shoulders, and the nation's emotions awaiting the outcome, investigators are scrutinizing the recovered wreckage for signs of mechanical failure or a bomb. How well they do will help determine what lessons the nation may need to learn about its air-safety system - and who any culprits might be.
Burn patterns and soot are being analyzed - a fuel fire leaves different scorch marks than a bomb. Traces of chemicals left in the luggage bay by an explosive provided the breakthrough clue in 1988 crash of Pan Am 103 over Lockerbie, Scotland.
In that flight, metal shards were also found embedded in the victims - indicating a blast.
Finding the cause of the Pan Am bombing "took what I think this [TWA] investigation will need - a concerted effort between the FBI, law enforcement, and information from the CIA," says an analyst who worked at the CIA's Counterterrorism Center during the Pan Am investigation.
So far, the TWA investigation is still in the initial stage. Investigators have found no sign of mechanical failure, although they have not ruled it out. Most experts, including the lead investigators, say indicators are pointing to an explosive device. Less than 1 percent of the plane has been collected.
At press time, it was hoped that the weather would allow searchers to send cameras and Navy divers down to explore what is believed to be a large section of the Boeing 747 resting on the ocean floor. The recovery of two recorders for cockpit conversations and flight data, the so-called black boxes, along with the plane's engines are considered crucial to unraveling why the aircraft exploded.
The search has been slowed as high winds and strong currents off Long Island have spread the surface debris miles from the crash site.
"Between the wind and the whitecaps, it's also become very difficult to see debris, most of which, so far, has been white, like the plane's inside panels," says Steve Branham, commanding officer of the Harriet Lane, the 270-foot US Coast Guard cutter leading the search operation.
But authorities are making progress. Specialists are conducting forensic tests on pieces of the plane, including a 35-foot section of one wing. With a spectrometer, scientists can analyze microscopic samples of soot or other chemicals and determine precise chemical composition.
Looking at the way metal is twisted also can reveal where the explosion took place and whether it was from a source inside the plane or from the outside - such as an engine.
The National Transportation Safety Board is officially charged with investigating the accident, but the FBI is looking into the criminal element. James Kallstrom, head of the FBI's antiterrorism unit out of New York, says he is waiting for that "golden nugget" of information to determine conclusively what caused the explosion.
If it is indeed a bomb, as most experts expect, the final investigative team will probably resemble the one put together to identify those responsible for downing Pan Am 103.
The CIA's Counterterrorism Center, in operation for 10 years now, brought together a "very tightly knit team," says Stanley Bedlington, a retired senior analyst from the Center. "We applied law enforcement work with intelligence work and just tracked down every single lead."
In that case, it took six days to determine a bomb caused the plane to explode. It was another four years before two Libyans were indicted in the case. They have not yet been captured.
The debris from Pan Am 103 covered some 3,600 square miles of land. Mr. Bedlington says they assumed the device was timed to explode over the ocean - but the terrorists miscalculated the time. That made the initial search far easier than the recovery effort now under way.
"The ocean itself, with its variable conditions and corrosive nature, makes it much more difficult," says Adam Wine, petty officer with the Coast Guard's emergency unit, known as the National Strike Force.
The winds and currents have already forced investigators to widen the search to more than 500 square miles. The area is broken down into grids, 10 to 100 square miles in size. More than 30 ships and planes scoured the grids last week. But over the weekend, the rough seas and need for rest forced the Coast Guard and others to cut back to less than 15 vessels and aircraft.
In the Pan Am 103 case, it was a collection of small clues that finally built the lead to the suspects. With the aid of Scotland police, investigators located the detonator device - a timer the size of a fingernail - as well as the suitcase that held the bomb with fragments of cloth still in it.
The seven-person intelligence team started with the fragments of the plane. Scientific tests on scrapings from the metal help determine the type of explosive used.
That, together with the timing device, enabled the investigators to reconstruct the bomb. The timer was a complicated system. A clock radio was used to set off another timer - a barometric pressure gauge that set the bomb off when the plane reached a certain altitude.
The timer was traced to a manufacturer in Switzerland, who had made only 12 of them. Investigators eventually matched it to a timer they found on two Libyans living in Senegal. The team traced the fragments of cloth in the suitcase to a clothing shop in Malta.
They deduced the bomb was placed on Pan Am 103 in Malta, carried over on a stop in Frankfurt, Germany, another in London, and exploded after take-off from there.
While forensic specialists concentrate on the recovered parts of TWA 800, other investigators are looking at who might have perpetrated a bombing.
"Our collectors and analysts would be looking into the backgrounds of people who were on that flight, who were on the same aircraft on its previous flight, and into any circumstances around its stop in Athens," says a senior intelligence official.
The Counterterrorism Center has a vast data base of names of terrorists, groups, and countries that support terrorism gleaned from sources worldwide. Intelligence officials also have alerted their collectors in the field to turn in any bits of relevant information. In addition, the National Security Agency is listening to about the last three weeks' worth of international eavesdropping. And every claim of responsibility that comes in has to be tracked down.