intelligence official is not ruling out terrorism. investigators are facing a daunting challenge tonight. there s a menacing terror group operating in the sinai which wants to bring down planes and but experts are also telling us there are mechanical and faulty repair issues which could cause a passenger plane to break up at that altitude. in the air for 23 minutes flying at cruising altitude flight 9268 was at a point where planes rarely break apart. the vast majority of airliner accidents occur on takeoff and landing. and cruise flight is really the safest portion typically. reporter: but tonight 224 people are dead. the plane s wreckage is scattered across eight square miles of the sinai desert, and serious questions are being asked. what about the claim from isis that it s responsible? we don t have any direct evidence of any terrorist involvement yet. it s unlikely, but i wouldn t rule it out. analysts say the isis