[datura]

Having been to Sharm where the plane took off from, and seeing the folks there, it is very likely that the baggage loaded on the plane has something extra in it. Either timed or altimeter triggered.

Since the tail of the aircraft separated, the structural integrity of the airframe failed - most likely from rupture. At cruising altitude, there is a huge pressure differential.

[Regulator]

it is very likely that the baggage loaded on the plane has something extra in it

Yup. Like the rest of the Third World, tarmac security is a joke. Half the baggers are probably ISIS or Al-Qaeda.

Either timed or altimeter triggered

Also dead on. I vote altitude triggered: it appears to have happened as they reached ~ FL300. Simple pressure differential detonator, set to typical cruise altitude pressure difference.

Explains everything, and is simplest: it's no accident that something like this happens to a Russian airliner in that part of the world at this point in history.

[McGruff]

The airline of the jet that crashed into the Sinai had not paid its staff in over two months, Russian news agencies have reported.

The widow of the doomed jet’s co-pilot, Sergey Trukhachov, said that he had not been paid for three months.

[RayChuang88]

If it is a bomb or SAM rocket, they need to immediately start looking for the chemical residue from explosives going off (that's how they were able to quickly identify the explosive material--Semtex made in then-Czechoslovakia--in the bomb that destroyed Pan Am Flight 103).