The aircraft was seen apparently flying normally yet a few minutes later impacted the ground vertically and partially inverted with wings and control surfaces apparently intact.
The aircraft was flying at modest airspeed speed, compared to more modern aircraft, in a mountainous area which was subject to winds measuring a significant percentage of the airspeed.
A sharp stall combined with an abrupt forward shift in the center of gravity of the aircraft accounts for the observed results. The exact details will be established by investigators, but this was an aircraft that was nearly 80 years old. It may have been in perfect condition but it was built to standards that were still being explored with single wings a novelty as an alternative to biplane wings!
A huge loss to aviation history and a great tragedy for all involved.