A recovery team dragging a sonar device beneath a boat on Saturday discovered a large mass of debris that could be the fuselage of TWA Flight 800.
The team was following a trail of wreckage on the ocean floor when the device smashed into something large. Today, investigators will drop video cameras beneath the water to see if it is the Boeing 747 jet.
Investigators were cautiously optimistic that the debris could provide vital clues about Wednesday's crash off the coast of Long Island.
"This is what we want," said James Kallstrom, the FBI's chief for the investigation. "We want the fuselage and the rest of the airplane. We want the metal so we can look at it forensically."
But Robert Francis, the vice chairman of the National Transportation Safety Board, cautioned that the sonar on Saturday did not indicate whether the debris was from Flight 800.
"While this is an enormously sophisticated piece of equipment, it's not sophisticated enough to tell us that this is the shape of an airplane as opposed to something that is out there from World War II."
So far, divers have recovered less than 1 percent of the jumbo jet. Although virtually everyone suspects a bomb, Kallstrom and Francis declined to say whether wreckage found so far showed evidence of what caused the explosion.
Autopsies on victims Saturday again turned up no evidence of burns or metal fragments that would be expected from a bomb. The Suffolk County medical examiner said 11 people have now been positively identified.
The investigation continued on two tracks Saturday, with the NTSB methodically treating the crash as an accident while the FBI gathered evidence for a criminal case. FBI agents have fanned out across Long Island to interview witnesses and have contacted security agencies in other countries to explore the possibility of a terrorist connection.
The slow pace has frustrated the families of victims, who complained that investigators are keeping them in the dark.
Ron Dwyer, who lost his 11-year-old daughter, Larkyn, in the crash, said he feared authorities were withholding information.
"I believe there is enough information to know what happened," Dwyer told reporters outside a hotel near John F. Kennedy International Airport.
"In my opinion, information is being withheld or suppressed until the (Olympic) Games are up and running so that the terrorists can't claim victory," he said.
Kallstrom said Saturday that he has a personal connection with Flight 800 because a close friend was killed in the crash. He declined to give a name but said it was a 25-year friend who was a member of the flight crew.
He met with families of victims Saturday and reassured them that the investigators would be responsive to their needs.
A small group of family members was taken by helicopter to the ocean site where Flight 800 went down and a videotape was made to bring back to the others, who have been sequestered since the crash at the hotel.
Joseph Lychner, who lost his wife and two young daughters in the crash, said it "helped me a great deal" to see where the plane went down. "I was trying to get as close to my family as I could," he said. As the helicopter circled the water, he said, he "did a little tribute" to them.
_ Information from Reuters and the Washington Post was included in this report.