Fighting post-mishap Sabotage Syndrome
From Chkbd, just above: "... if the investigation result had determined a missile attack as the probable cause ... people would be crying 'Conspiracy! Boeing and FAA cover up centre tank fuel explosion!!'"
That's just what "accident" investigators were up against, from the very beginning. Metal wreckage was on the ocean floor -- and a Respected Pilot Gossip sent an email outlining the detailed missile scenario. That did it: the whole story was right there on this new thing called the "web". The missile scenario must be true, it was on the web (while the direct evidence was still on the ocean floor).
Much later the wreckage was recovered from the bottom of the ocean, and law enforcement agreed that there was no evidence of "detonation" anyplace on the wreckage. Everyone agreed that there had been a "deflagration" inside the near-empty center tank. On day two we had told the FBI about the sister-ship's inflight breakup over Madrid in May'76.