Local sources are saying the pilot initially requested a climb to FL360 then made some comments about being low on fuel, subsequently requested descent to FL340 and then a rapid descent occurred with communication to FL120 thereafter the rest is history. There is a lot of speculation, however, the lack of coms tends to suggest some sort of pilot incapacitation and locals apparently reported seeing a jet "spinning " i,e stalled. We may never learn the real cause, very sad for such a happy event to end in this manner.