If I recall correctly the exact cause of the crash was never discovered but one can draw conclusions
I believe they did eventually get to the bottom of that one. The resources put into establishing the cause certainly point to how seriously the whole thing was taken. The hunt for bits on the sea bed lasted 14 months and involved 46 ships. No less than 592,610 pieces of wreckage were recovered from 11,069 deep sea trawls.
At the end of that it was decided that the first bit to separate was the starboard wing tip pitot head (due to a fatigue fracture) which led to a low speed signal being fed to the auto mach trim actuator and the stall detector thus lowering the elevators and the leading edge flaps.
The aircraft progressed into a high speed dive from 54,000 ft. Partial structural failure preceeded the impact with the sea off St Brides Head at .855M. The Captain ejected unsuccesfully just moments before impact.