I do not think a wilful act other than a head case individual or even crew member stacks up!
Any organised terrorist group would have claimed their prize by now as not to do so would be unproductive in their misplaced eyes to their cause.
More likely this was a case of massive depressurisation. Note the private jet accident which flew for miles with all the crew and PAX inert in their seats.
a massive decompression would have accounted for the lack of radio communications, attempt to change course, deviation off track and eventual crash in the Sea.
Seems to fit the events more than some high tech terrorist attack