The investigators said bureau agents and immigration officials had repeatedly failed to investigate or find the foreign visitors and warned that they might still be in the country.

The investigators warn that the uncertainty and haste make it more likely that the system, once its pieces are linked, will balk when put to actual flight tests.

But the board's investigators warn that they may never find the precise trigger for the Flight 800 explosion.

One example is from August 1993, when a special investigator warned, eight months before it began, that genocide was likely in Rwanda.

No suspects were captured at the site, but investigators did find an AK-47 assault rifle, and warned the public that the suspects could be armed and dangerous.

While virtually all the prosecutions so far have proved successful, investigators have long warned that every passing year makes it more difficult to build a case.

As Mafia rackets in construction and trash-removal fade, investigators warn that a new crop of mobsters is focusing increasingly on lucrative white-collar crimes.

But the investigators warned that the reviews "do not provide the same level of assurance as an audit, and should only be used in conjunction with audits."

For more than a decade, federal investigators have been warning that the precautions against the hijacking or bombing of airplanes were inadequate and could be easily circumvented.

Partly as a result of the new radar information, investigators warned tonight that they might never find any large pieces of the plane.