He had a reason in his own mind at that set of moments, but there is no excuse for killing all aboard for any reason, go kill yourself on your own time, no need to be a prick and kill everyone around you too is there.
As there doesnt seem to be any islamic conversion angle so far then I reckon it was something stupid like he didnt get on with the pilot and there was some final straw that made him snap and all the way into the ground the pilot failed in some maddening sense to say or do the "right " thing to make him stop.
That is just a guess, although it is more odd that he didnt seem to say a word all the way down, which i think he would have done if he was angry at the pilot, so maybe scratch that idea and plumb for some kind of psychotic break.
I guess they will figure out a likely reason soon enough.