Indeed the selected altitude was changed at 09:30:55 from 38000ft to 96ft. This is picked up by the ADSB/ModeS rader system which covers all of France. The noise of this switch change would have been picked up by the voice recorder and they would then have been able to directly correlate the SelAlt change wth the switch noise. This is why they are [almost completely] certain it was a delieberate act.