The rumour is that the plane was shot down by a US Navy missile. The mouth belongs to Pierre Salinger, former spokesman for President Kennedy and until 1983 a reporter for ABC television. At a convention of airline executives in Cannes on Thursday he said he had documents proving "friendly fire" was to blame. "The truth must come out," he said, brandishing two pieces of paper, allegedly written by an American but handed him by a French agent.
The papers, which he has offered to surrender to the FBI, describe how a Navy ship off Long Island fired a missile, believing no commercial traffic was flying below 21,000 feet, when in fact TWA 800 had reached only 13,000 feet.
Yesterday Mr Salinger said he received the papers five weeks ago but had been approached by "very important people" asking him not to release them until after Tuesday's presidential election, for fear the disclosure would alter its course. "If the news came out that an American naval ship shot down that plane it could ... have an effect on the election," he said.
The FBI denied the implied cover-up. James Kallstrom, the assistant director leading the inquiry, said investigators "have absolutely not one shred of evidence that it happened or it could have happened". A White House statement said: "We have ruled out the responsibility of friendly fire." Of three scenarios still being considered - a bomb detonated on board, a hit by a missile, or mechanical failure - it is the last that has been gaining ground recently.
Attention has focused on the possibility that fumes in the plane's central fuel tank ignited and triggered an explosion. This week investigators disclosed that, with 95 per cent of the plane reassembled, there was no place in the fuselage through which a metal rod could be passed and through which a missile might have travelled.
Mr Salinger may well be genuine in wanting to help resolve the investigation. But whether he knew it or not, he was also pushing at a series of open doors.
Instantly receptive, for example, will have been his immediate audience. The airline industry would like nothing more than for evidence to surface absolving it of responsibility for the crash. A finding of mechanical failure would instantly spell lawsuits.
For the wider public, Mr Salinger might as well be offering chocolate to children. The fate of TWA 800 long ago attained unsolved-mystery status and, like all mysteries, it is a breeding-ground for conspiracy theories. And they do not get much better than this one, suggesting the killing of American citizens by their own government and a cover-up at the highest levels.
But less excitable souls might ask the obvious questions: what motive could there be to try to smother so terrible an event? And could a cover- up have worked so effectively, with many agencies and the military involved in the investigation and every US news organisation sniffing every angle?