Sequence reads;
0327 ATC tries to contact aircraft some 2 minutes from FIR boundary, and one assumes continues to call on working freq and Guard for next 2 mins or more.
0329 a/c crosses FIR boundary with no response to ATC - something is amiss in board.
40 seconds later something triggers a turn and rapid descent.
That ain't no coincidence the timing is just too cute. Looks like someone is out to deliver a nasty message to Egypt by the looks of it.
The turn and descent look not unlike a rapid depressurisation drill, not an unreasonable possibility after unlawful interference of a violent nature.
The FDR will be quickly recovered in those depths. We'll know soon enough.