US investigators have yet to come up with an explanation of why a Boeing 737 plunged to earth over Pittsburgh in September 1994, killing all 132 people aboard.
The task of solving the mystery of Flight TWA 800, which crashed last Wednesday killing 230, would seem to present an even greater challenge.
The Boeing 747 exploded over the Atlantic Ocean, scattering the wreckage over what investigators say might be 500 square miles of sea to depths of between 100 and 200 feet.
A lot of extraordinarily difficult preliminary salvage work still lies ahead before the National Transportation Safety Board (NTSB) and the FBI are in a position to examine the evidence.
By yesterday, despite a massive deployment of resources, only one per cent of the airliner's remains had been recovered 130 bodies remained unaccounted for and of the 100 bodies recovered, only 10 had been positively identified.
The two black boxes containing the flight data recorder and the cockpit voice recorder have not yet been located. The airliner's fuselage, which investigators hope will contain much of the evidence and most of the missing bodies, may have been found on Saturday by a navy sonar device.
"They have found a trail of material on the bottom," said Robert Francis, the NTSB vice chairman heading on site investigations into the crash. "And that trail culminates in a large piece of something under there." Despite the lack of evidence, investigators have made it plain in their public statements, and in their off the record asides to reporters, that they believe TWA 800 was downed by a bomb.
"The chances that this is mechanical are slim," said Mr Jim Kallstrom, the director of the FBI joint anti terrorist task force investigating the crash. "The least likely thing, minus the forensics - which we are waiting for - is mechanical. That's just common sense." Why is it common sense? Clive Irving, a New York based British author who has written a book about Boeing and the 747 articulates what has become conventional informed opinion.
"There is no previous example of a complete and instantaneous catastrophe involving a 747 that was not a bomb," Mr Irving said. "If it had been a structural failure, the degree of disintegration would not have been so sudden especially if you take into account the sheer size of the 747." But the means employed by the presumptive "cowards", in Mr Kallstrom's words, to blow up the airliner remain at this stage an unfathomable mystery.