BACK IN THE 80S, I used to investigate major aircraft mishaps and ever since those days, I've kept a kit bag ready to go in one of our closets. I've considered what I might be doing if my duties took me to the remains of the Russian Metrojet passenger Airbus 321 (A321 on Flight KGL9268) jet that crashed in Egypt’s Sinai Peninsula with 224 people on board on 31 October. 
Before our crash team left to investigate a remote destination, we would have reviewed easily-accessible materials. Satellite imagery shows no missile heat signature tracking near the aircraft's flight path, hence an airborne strike can be discounted.
Our mishap team would take a quick overflight of the wreckage. We would see the vertical stabiliser is bent at a 90 degree angle. The aircraft's rudder is missing from the main crash scene and there is no trace of the rear one-third of the vertical stabiliser (the section that was closest to the rudder). The horizontal stabilizers are missing too.
The maintenance specialist on our mishap team would have Airbus drawings (above). Those drawings show the whole A321 tail cone subassembly is bolted to the rest of the empennage via attachment lugs at four points. None of those large lugs is visible in the crash photos. Photo below from TylerMonkey on PPRUNE (#581). A close-up photo shows clear details of the tail cone's front firewall. You would expect to see a set of lug nuts in the top left of the photo (in the position of the triangular hole in the outermost frame). You can also surmise important information by reading the kind of metal damage to many of the aircraft parts scattered on the ground. Some key portions of the metal are bent outwards. In other segments, the metal is sheared in a manner of a clean tear. When physical objects are correctly interpreted by structural experts, they enhance the credibility of electronic data signals gathered by other accident investigation specialists.
One of our mishap team members would attend the analyses of the Cockpit Voice Recorder (CVR) and Digital Flight Data Recorder (DFDR). The analysis of these two data sources would be synchronized and key data points would be cross-examined. CVR/DFDR data alone can determine the origin of the mid air break-up. If a bomb exploded onboard there would be a sudden increase in delta P (shockwave) followed by a fast increase of cabin altitude due to structural failure. If the aircraft structure failed, there would be a sudden increase in cabin altitude and falling delta P. These data sets will help substantiate the physical evidence and show that the A321 broke apart in flight. The crash site has debris from the tail section far removed from the rest of the fuselage, suggesting that section may have split off in the air. The midair breakup left debris scattered over approximately eight square miles, the head of the Russian-led Interstate Aviation Committee, Viktor Sorochenko, told the Wall Street Journal. 
One week after the crash happened, intelligence officials vetted several details that suggest an explosion brought down the aircraft. The sound of an explosion can be heard on the black box recorder of the downed Russian jet, according to reports in France on France 2 TV channel. An unnamed investigator with access to the black box says the explosion can be heard on the cockpit voice recorder. This sound supports UK intelligence that a bomb was smuggled into the hold of the Metrojet plane.
In separate intelligence channels, US officials reported chatter between Islamic State leaders in Sinai and Syria about the Egypt plane, and discussions included boasts about taking down an airliner and how it was done. The UK intelligence community also found evidence of a major plot in intercepts picked up during a review of the disaster.
Attention will certainly focus on flightline security and the relatively easy movement many local people enjoy on the Sharm aerodrome.
1. Professional Pilots Rumor Network -- "Airliner missing within Egyptian FIR", last accessed November 2, 2015.
2. Robert Wall -- "Probe of Russian Plane Crash in Egypt’s Sinai Points to Breakup in Flight" in the Wall Street Journal, November 2, 2015.