15 years ago today, on the eve of the 1996 summer Olympics in Atlanta, U.S.A., the crash of Trans World Airlines (TWA) Flight 800 killed 230 passengers and crew, and it remains one of the world’s major aviation mysteries. The government’s $40 million investigation concluded that the Boeing 747 was probably brought down by what it described as a fuel tank explosion, leaving the origin of the explosion unidentified. The case was closed on that tenuous outcome.

But two days after the plane exploded, Utah Sen. Orrin Hatch, who had been briefed by the federal government, had told CNN: “We’re looking at somebody who either put a bomb on it or shot a missile, a surface-to-air missile.” For years, government investigators tried to have it both ways; the National Transportation Safety Board (NTSB) was acting under the direction of the FBI, which was involved on the premise that a “crime” may have caused the blast, though the FBI refused to confirm or deny the existence of criminal evidence.

The CIA, in an extraordinary departure from usual government procedures, made a highly publicized video (pictured in the image, above right) to counter the missile theory. But radar records of the area in which the plane went down picked up four unidentified tracks and showed that one of those tracks, according to the NTSB, is consistent with a surface vessel moving at 30 knots; it was within three nautical miles of TWA 800 when the 747 exploded. Notably, the NTSB reported that the radar track, which remains unidentified, continued to move after the plane broke apart. Nearly every boat within miles had rushed to the disaster area to assist rescue efforts. Not this vessel, which was underneath TWA 800 when it exploded. The mystery remains.