High-tech Navy sonar located more wreckage from TWA Flight 800 than investigators had thought remained on the ocean floor.
"Hopefully, one or more of those pieces are going to hold the key to what caused this horrific tragedy," a source told the Associated Press on Thursday.
Meanwhile, another source close to the investigation played down a Washington Post report today that tests on plane debris point to a mechanical failure as the cause of the July 17 crash.
Senior investigators told the Post that analysis of center fuel tank debris shows damage patterns consistent with a slower, less energetic explosion than would be produced by a bomb or missile. The paper did not identify the sources.
The AP's source confirmed that such "low order" damage patterns are present on the fuel tank debris but said no conclusion can be drawn.
"We still have no clear picture as to what caused the tank to explode," the source said. "We don't know if it was a secondary or primary explosion."
While some of the center fuel tank debris shows signs of having been blown outward, other parts of the tank appear to have been bent inward, the source said.
National Traffic Safety Board spokesman Peter Goelz said: "We don't see any evidence of a high- intensity explosion yet, and we don't see any clear external source of ignition. But that doesn't necessarily eliminate a bomb or a missile. We're still trying to figure out why the center fuel tank exploded. That's the mystery that has us all stymied."
Divers have recovered more than 90 percent of the Boeing 747 and more than 80 percent of the center fuel tank, which exploded moments before the Paris-bound jet plunged into the Atlantic Ocean off Long Island. All 230 people on board were killed.